Infected w/Security Center 2012 virus, now no internet!

I was infected with Internet Security 2012 (twice). In the cleaning up process, we ran 3 different anti-spywares for cleanup. Avast (downloaded from MajorGeeks) did a fabulous job...at first. After cleaning with Avast and surfing the web, I shut down for the night, when I started up again the next day, the computer ran a "check disk" and that was the last of the internet.
We have tried everything, even uninstalling Avast, then re-installing it. All we get is "No TCP/IP connection".
There seem to be similar problems on the forums, but not one precisely like mine.
I also have only the OS disk, no Windows Office installation disks (we kind of pieced this computer together), so stripping the computer back is not much of an option.
I'm running Windows XP on a Gateway laptop MX-6960.

Any help with a fix, or at least where to look for additional help is greatly appreciated.