Hi,
Try Booting in Safe Mode or Use Last Known Good Configuration.

>I have a PC that I think is infected with a virus. The symptom is that I cannot get it booted up into Windows XP. It keeps saying
>
>svchost.exe - Application Error
>
>An attempt was made to execute an illegal instruction.
>
>I downloaded a program to use to fix it, supposedly, but if you can't even boot up the machine, how do you then use a program to fix the problem? Catch 22 situation.