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Computer Repair with Diagnostic Flowcharts
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Copyright 2012 by Morris Rosenthal
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DSL, Cable and Dial-Up Modem Diagnostic Flowchart
Warning! You must unplug your ATX power supply from the wall before working inside the case.
I imagine over 95% of PC's are connected to the Internet these days, at least, they're connected when the modem works. Most people today have broadband modems, cable or DSL, but in rural areas and hill towns and high-cost areas, it's still not uncommon to connect via a dial-up modem. The troubleshooting flowchart for Internet connection problems is one of seventeen flowcharts from "Computer Repair with Diagnostic Flowcharts Revised Edition." If you find the approach as useful as many thousands of other home hobbyists and professional techs, you can order the book through any bookstore, or instantly download the 120 page printable ebook.
Troubleshooting PC Internet Connections
Note that these steps correspond with decision points on the flowchart and are reached directly by clicking on the diamond symbols. The text below cannot be read sequentially.
Does the Internet connection employ DSL (Digital Subscriber Line) or the cable TV network? High speed Internet connections are rarely built into desktop PCs, so an external broadband modem or broadband modem/router is needed, generally supporting multiple PCs and laptops within a home or business. The "free" modems supplied by the phone company or the cable company are often limited to a single connection, so you need to purchase a router for additional wired and wireless connections. I bought a friend a wireless router that also supported four wired connections at a WalMart for $30 last month, worked great throughout a four floor house
In many areas of the country you can now buy a cellular modem with no contract for mediocre broadband, better than dial-up but slower than wired service. I haven't added troubleshooting for these USB devices to the page because either they work or they don't, it's just a question of the software installation and being in range of a cell tower.
All broadband modems are manufactured with a cluster of diagnostic LEDs that report the status of the connection to the ISP and the modem activity. The most important LED is the one that tells you if the modem is connected to the Internet. When you first power on the modem, this is generally the last LED to settle into a steady state as the Internet connection is negotiated. Both DSL and cable modems may also include an LED that reports whether there is a live connection (ie, electrical connectivity) to the phone company central office or the cable network, whether or not you have Internet access. If this connection link LED is red or doesn't light at all, you're not going to get Internet access because the circuit isn't complete. If the Internet LED is red or doesn't light, that means an Internet connection couldn't be negotiated. The first thing to try in both cases is to power down your PC, power down the modem, wait a minute, restart the modem and then restart your PC. Check that none of your cables have pulled out (especially with DSL modems where the phone jacks can separate pretty easily) before you call the phone company or cable company to see if service is interrupted in your area.
Are you using a cable modem? The troubleshooting flowchart branches here because cable modems are less complicated to troubleshoot than DSL modems due to fewer failure points. You might notice that for cable we skip the step of swapping modems with a friend using the same service. Cable modem are much less likely to work if you move them from location to location because cable companies have all sorts of schemes for preventing piracy, and you may find you need them to reprogram a modem to get it to work on a different account. If you are experiencing intermittent signal failures with a cable modem, there's a good chance it has to do with wind or weather disrupting the connection outside your house. But it also pays to shorten the path from the cable modem to the interface installed by the cable company as much as possible, as every connection and splitter inside the house results in a drop in signal strength and increased electrical noise.
DSL modems require you to install high frequency filters on every other phone connection that uses the same circuit (phone number) that the DSL modem is using. If you don't install the filters, you'll get background noise whenever you talk on the phone that degrades with Internet activity. Worse than that, some intelligent phones, fax machines and answering machines create their own digital traffic on the line, interfering with the DSL modem so it can't negotiate or maintain an Internet connection without the filters being installed. Any time you are setting up a DSL modem for the first time, if it can't negotiate an Internet connection after the phone company reports that Internet access has been turned on, you should unplug every other device using the phone circuit to see if that makes a difference. If it does, you can easily work out the problem device or the faulty filter by process of elimination.
The easiest test to see if your DSL modem has failed is to borrow the same model from a neighbor who uses DSL from the same phone company. If the modems aren't identical, it may still work without any software installation, it's just easier if they are the exact same model. If you don't like asking to borrow a modem, you can do the opposite and bring your modem to their house and connect it in place of their own. The point is to isolate the problem to the modem or the phone wiring.
In cases where your modem only offers a choice between a single network port and a USB port to connect your PC, try uninstalling the software, connecting by the other method (ie, the one you weren't using), rebooting, and reinstalling the software. If you're using the USB connection, try swapping out a known good USB cable from a printer or any other USB device. If you're using the yellow network cable with RJ-45 connectors, see if you can dig up one from the past to try, as they get shipped with all sorts of modem and router devices. If your modem includes a multi-port router, connect the cable from the PC to a different network port. Just because the LED link light for the port is lit doesn't mean that it's working, it's just a continuity test for power. If you've only tried to connect via a wired PC and the router includes a wireless capability, enable wireless and try connecting with a laptop or a WiFi Kindle, anything that could confirm that the Internet connection is good, and therefore, your PC networking link is the failure point.
When any one of the alternates above work, like taking the modem to a friend's house or successfully connecting to the Internet via wireless, it reduces the possible problems to your PC. You can certainly test the USB port if you've connected via USB, testing the network port would require a networkable device, but if you've swapped cables and Windows claims the network adapter functioning, it probably is. The remaining issue is software, either the installation of the software supporting the modem or the presence of other software on your PC preventing it from working. The main culprit is usually fire wall software blocking Internet access, and other than disabling the firewall, it can be very tricky to troubleshoot. If you can stand waiting on hold, try calling the technical support line of your Internet service provider and they should be able to take you step-by-step through all the possible choke points.
Did the modem take the phone off hook and dial? PC modems always include a tiny speaker that's good enough to hear the dial tone and to listen to the phone dialing. If you aren't sure if the volume is on, go to Control Panel in Windows and check the modem properties. If you're using a laptop computer, the modem sound normally plays through the speakers, so make sure the regular volume control is turned up.
Do you hear the ISP modem connect and negotiate with your modem (whistling and hissing). If the modem on the ISP end doesn't pick up, double check the phone number you are using. To check if the ISP is working, you can dial the phone number from a voice phone and see if their modem picks up and tries to negotiate with you!
Modems aren't any smarter about outside lines and prefixes than regular phones, so if you need a dialing prefix to connect from your regular phone, make sure the modem is using it as well. If you work in a business, try dialing out over the fax line, which will have a clear path through any PBX equipment. Dialing "9" to get out of a PBX is common, and for a modem prefix, add a couple commas after the "9" to introduce a delay and allow for the outside line to be connected. Of course, if the ISP phone is busy, that's a problem on their end, and they may just not have enough function modems in their pool.
Finally, if your modem dials but instead of trying to connect a call, all you hear is the dial tone followed by a recorded message from the phone company that your phone is off hook, it means your line was set up for an old rotary pulse dialer, while the modem is using the modern push button tone system. You can change from "tone" to "pulse" in the modem properties which can be found through the Control Panel icon in Windows.
Does your dialer software kick back with an error message like "bad protocol" or "can't connect" after you hear the ISP modem pick up? These errors tend to be so vague that they could mean anything from a mistake typing your user name or password, to the fact that your service was cancelled because you didn't pay the bill. If you've connected with the same modem before, try redialing a couple times through the course of the day to make sure the problem isn't just noisy phone lines or bad modem in the ISP pool.
Can you confirm that your account information and password is correct by refering to correspondence from the ISP or by contacting them over the phone? If you have the password and the login name correct and these have never changed, it's unlikely that the problems are due to specific modem settings (unless you made changes). If you can connect at some times and not at others, the problem is almost certainly due to line conditions cropping up from weather, heavy phone traffic at a certain time of day, or randomly hitting faulty modems in the ISP's modem pool. Wet weather is a killer for old telephone company infrastructure, as is windy weather.
Can you get an Internet connection if you lower the modem speed? You may have to search the Internet for a command line control string to do this since the changes to the speed done through Windows Control Panel aren't always effective. I know you don't want your slow dial-up connection to work even slower, but it's a good troubleshooting test. If you can connect at a lower speed, move to the flowchart for modem performance
Have you tried connecting to another ISP? If your modem dials, whistles, all the good stuff, and you still can't get a connection, the fault may be with your ISP. If you can find a CD from another service kicking around, AOL or whoever, you can install it just to find out if the modem will connect to their service. You don't need to sign up with them for this test, if it gets to the point that they are asking for your credit card, you'll know that the modem is working fine and you can quit.
If you get a message stating "No Dial Tone", it means that you plugged the phone wire into the wrong port on the modem or the phone wire isn't live. The proper port on the modem to connect to the patch cable to the wall jack is labeled "line." The jack labeled "phone" is for connecting a voice phone to the modem to save you from needing a splitter. To test that the wall jack is good, connect a regular phone and see if you get a dial tone. If the wall jack is live and the PC doesn't report a dial tone, swap out the phone patch cord from the modem to the wall jack, and if that doesn't do it, the modem is bad.
Has the most recent software driver for your modem been installed? Whether your modem is an add-in adapter or integrated on the motherboard, you should be able to find the latest driver on the manufacturer's website. As with all add-in adapters, modems often sit on the store shelf for many months or even a year or two before selling, so the fact you just bought it doesn't mean you got the most recent driver software in the box.
Does the modem show up in Device Manager without any problem reports? If Device Manager reports anything wrong, an exclamation mark or a question mark, the first step is to reinstall the latest drive. You really shouldn't run into Interrupt Request (IRQ) conflicts on recent PC's with plug-n-play operating systems, and most add-in modems no longer come equipped with jumpers for manually setting the resources. If you do have a conflict, try uninstalling the modem, going through a reboot cycle, shutting down and reinstalling, and see if Windows can sort it out. If not, see the troubleshooting flowchart for conflict resolution.
Did Windows report that the modem was already in use when the software tried to dial? The first thing to do is shut down, reboot, and see if the problem fixes itself. Next, try using the "More Info" option for the modem which is reached through the Modems icon in Control Panel, under the Diagnostics tab, to see if Widows believes the modem operational. When the port is reported as already in use, it means Windows thinks that another program is using the modem. This isn't a common error anymore but in the old days, it sometimes happened that other serial port users, like the original digital cameras or the personal data assistants (PDAs) that have been replaced by smart phones, used poorly written software that took over the modem's resources on boot.
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