|Difficult to tell what happens in a virus attack.|
Could try a repair using the cd.
Personally I'd start all over and just load the whole os and apps back on.
If you must, use a live linux cd or make a barts PE disk to get your files off. Be warned that they may be damaged or infected.
Could use a ultimate boot cd to use some of the tests. See memtest and hard drive diags just in case it is a hardware issue.
Why did it take me over a year to phone in a problem to ATT?