Diagnosing Net Connection Problems

Monday Oct 27th 2003 by Ronald Pacchiano

Have a network with one or two PCs that can't connect to the Internet or other networked computers? This week we look at several tips and tricks of the trade that could help you diagnose and fix computer connection issues.

I have a small network made up of four computers. All of the computers are connected to a NETGEAR DG814 router via Ethernet cables. Three of the computers on the network are set up and working fine, but I'm having problems with the 4th computer, a Sony VAIO PCG-FX103 notebook.

For some reason the VAIO is incapable of seeing any of the other computers in the workgroup or browsing any websites. I can't even "Ping" the router from the notebook. I'm fairly sure the cable is good because the light on the card and the one on the router itself are both illuminated.

One strange thing I did notice however was that WINIPCFG was reporting that the PC is using an Internet protocol (IP) address beginning with a 169. My router's dynamic host configuration protocol (DHCP) scope is supposed to be assigning IP addresses of 192.168.0.x. I tried manually setting the IP address to, but that didn't help. I've tried as much as I can think of (renewing IP address, adjusting settings, etc.). Do you have any ideas what else I might try?

I'm not surprised that the system didn't work even after you manually entered the correct IP address information. Typically the only time you would get an IP address beginning with a 169 is when the PC is not communicating with the DHCP server. So if it's not communicating with the server, entering the correct information isn't going to help.

There are a number of reasons why this might happen, with the most obvious being a physical problem with the network adapter itself. Just because the link light is lit doesn't mean the card is working properly or that the cable is good. Also, you could try moving your cable to a different port on the router. Ports don't go bad very often, but it is a possibility.

Now if you're on a wireless network, there could be a million possible causes for your problems. However, since you are simply connecting a single PC to a router via an Ethernet cable, the possibilities are much more limited.

In my experience, when this situation comes up, the majority of the time it has to due with some type of problem with the transmission control protocol/Internet protocol (TCP/IP) stack. Usually some aspect of it has become corrupted, and the entire stack needs to be reinstalled as a result. The process varies from one operating system to the other, but basically what you would need to do is go into your network properties and remove all of the networking components that are installed there.

This usually includes things like the Network adapter drivers, the various communication protocols (e.g. TCP/IP, IPX/SPX, NetBEUI), and the network client. Once all of these items have been removed, you'll be forced to reboot the system. After the system reboots, reinstall the network adapter drivers, which should also install any additional components you might need. After the system reboots again, your TCP/IP protocol stack should be functioning correctly once again.

One thing you might want to consider doing before all of this is to verify that your PC hasn't been infected by a virus. There are numerous viruses out there that could disable your PC's communication capabilities, so I would recommend first downloading the latest virus definitions and thoroughly scanning your system.

If all else fails and neither of these suggestions work, you might have to consider wiping out the PC and reinstalling the operating system. Sometimes a Windows system can become so saturated by poorly written software (not to mention things like adware and spyware) that it can just become completely unstable and have a detrimental effect on the performance of various systems. Sometimes this includes network communications. While I admit that it is a major hassle and inconvenience to redo it, I can almost guarantee that it will solve your problem.

I have a computer on my home network that has been accessing ICQ, e-mail, and the Web without problems up until the other night. Today when I turned the computer on, it could no longer access the Internet. Every time I try to go to a site, I get an error message saying the page is unavailable. Yet for some reason applications like ICQ and KaZaA Lite are still functioning, and even my e-mail is still working.

So far I have tried a number of things to correct the problem. I have tried dropping and reinitializing the IP address on the troubled machine using IPCONFIG. I've tried resetting the router. I performed a virus scan using Norton Antivirus 2002, but as of yet, nothing has worked.

I tested the LAN connection with a spare laptop, which worked fine, so I think the problem is definitely because of something on the PC, but for the life of me I can't find it. I thought that Internet Explorer might have become corrupted, so I tried reinstalling it, but that didn't help either.

My home network is made up of a couple of switches and a network address translation (NAT) router connected via a Comcast cable modem, and the offending PC is running Windows XP Home Edition. Please Help! I am out of ideas and getting desperate.

You're right in assuming that the problem lies on the Windows XP Home system. If your laptop is functioning properly (as you indicated) off of the same router, then the problem is neither with your router nor your Internet service provider — it must be with that specific PC.

We know that you do have a working Internet connection because ICQ, KaZaA Lite, and your e-mail are all functioning correctly. So it sounds to me that the most likely cause of your difficulties might be because the browser on your wayward machine was somehow configured to use a proxy server.

If it is and there is none present, you won't be able to get out to the Net. A proxy server is normally used in a business — it sits between the client users and the real server that lets you out to the Internet. It can be used for security purposes or to speed up browsing by caching frequently visited Web pages, or both.

This is a very simple problem to rectify and can be done in just a few minutes. Launch Internet Explorer and then select Tools, then Internet Options, and then the Connections tab. Click the LAN settings button toward the bottom of the window. You'll probably find a check mark in the box labeled Use a Proxy Server for your LAN. Clear it and close Internet Explorer and open it again. Now re-launch Internet Explorer, and you should once again be able to browse the web.

It's hard to say how this box got checked in the first place, but it was probably done inadvertently and should not recur the next time you reboot your machine.

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