Network says it's connected, but it's not

[Jephph]

I've got a computer that can't get online. There are many things I've tried, but this one's pretty tough. The computer says the LAN is connected, and the network adapters are functional in Device Manager. Here is a list of things I've done/checked:
*Checked basics like "Automatically detect settings" under LAN settings and Obtain IP Address Automatically and Obtain DNS Server automatically.
*Used IE and Chrome, and tried updating programs online.
*Other devices connect fine to router. I tried powercycling both the router and modem. The computer also has a wireless PCI card, so I tried that as well. It shows as connected, but still nothing. Also tried different router and modem. I can't get into the router settings either. Also tried different ethernet cables.
*Ran malware scans with Spybot and Malwarebytes. Couldn't update Malwarebytes, got "database is missing or corrupt" error.
*Ran AVG Scan
*Tried Safe Mode with Networking
*Winsock fix
*lspfix
*System Restore
*Turned off Zone Alarm
*Temporarily disabled AVG
*Network Diagnostics gives "Contact the company that provides you Windows XP Product Support"
*Commands: netsh winsock reset catalog, netsh int ip reset reset.log, ipconfig gives "An internal Error occured. The request is not supported.
*Thought maybe AVG moved a network file to virus vault so I restored some infected files.

Any help is much appreciated.

 

[Jephph]

I think I've found the culprit. When I was checking services, and noticed that DHCP, DNS, etc. were not started, I went to device manager, clicked "show hidden devices" and under non-plug and play drivers, "IP network address translator" and "tcp/ip protocol driver" had yellow exclamation marks on them. I uninstalled tcp/ip protocol driver thinking that it would reinstall it automaticallly on reboot, but it didn't and now I have no tcp/ip protocol driver in device manager, and still can't get online.
I know I've caused more trouble, but at least we know the problem now. Again, any help is greatly appreciated.

 

[Ghiedo27]

Have you tried entering Netsh Interface ipv4 install from the command prompt (reboot req)? Does TCP/IPv4 show up in local area connection properties?

 

[Jephph]

I get "the following command was not found: Interface ipv4 install"

Internet Protocol (TCP/IP) shows up in Local Area Connection properties. There is no TCP/IPv4. It is a Windows XP Professional system if that makes a difference.

 

[mammador]

If you run different Internet services/applications, like VoIP, web, e-mail, etc. does the same thing result?

It may not be a problem on your home network, but at the ISP's end. If you are sure there are no issues in your home network (whether router, workstation, Ethernet cabling, NIC, etc.) then contact your ISP to see if they have a fault at their end.

 

[Jephph]

sfc /scannow did the trick!