First, try a virus and spyware scan. Those probably wouldn't cause it, but you can't go wrong with doing those things as a sort of general remedy. If you don't have scanning stuff, go to http://www.lavasoftusa.com/software/adaware/ and
http://housecall.trendmicro.com/ for spyware and virus scanners, respectively.
After that, you can try the thing that's most likely to help. Doing a system restore will nearly always clear up a problem like that. You can find that in a folder that's usually called system tools or something like that. Start < programs < accessories < system tools. (for me.) Just pick a date to restore to that's before this problem started occurring.
Oh, and on the off chance that you know what you're talking about when it comes to computers, and have already tried all this stuff, I apologize.