You need to run a scan.. for more super hidden viruses you'll need to dig deep like with Neuber.com's Security Task Manager.. shows all programs active and gives it a threat rating.. I found a virus I installed intentionally that goes invisible as super super hidden admin permissions. Nothing else would deactivate it. Once i knew the virus name from MSE scan, I removed it then repaired edited registry info. This program comes with an anti-keylogging feature that stays active when you turn your PC on.
This wont find some of the new viruses but a good free scanner is Microsoft Security Essentials
otherwise check out Kaspersky Free Virus Download page and who knows maybe you've got the new TDL-4. Hope not. Article is
here. Fixes are
here.