Possible virus or hacker

IE repeatedly sets it's homepage at something
called "about:blank" and pops up with an ad for spyware
detecters. Also, certain system files are missing or
corrupt. I've run virus scanners, spyware detecters,
scandisk, sfc and dr Watson. Neither detected anything,
however dr watson gave me this message:

--------------------
unknown has altered Windows system files.

Module Name: unknown


I also tried online v-scans from mcafee. I'm out of
options at this point. Is there anything else I can try?