I seem to have this odd problem, endemic to all the computers I've owned. If I have a utility that requires all the drives to be scanned, it will fail. I actually went nearly a decade without ever successfully defragging ANY drive - not for lack of trying, mind you (eventually AusLogic's disk defrag program finally did the trick).
Virus scans, or any stuff like that, like only seem to work if I shut everything down, unplug from everything and scan from a fresh startup, sometimes in safe mode. So while I use Windows normally, my preferred tools for scanning for problems has been a Linux-based boot disk (this is about the very limits of my incredibly meagre Linux skill, FYI). I don't know why. When I finally do get a clean scan, I never have any bad viral problems or similar. It's not like I'm one of those idiots whose computer becomes a station wagon full of drunken trojans without my ever noticing - I tend to have good instincts for smelling problems.
I actually HAVE an old Linux OS-runs-from-drive disc somewhere, but it's pretty out of date and had no onboard anti-virus program.
One of my far more knowledgeable friends said that it's 'because I use my hard drives much more intensively than most users" (I save and re-save lots and lots of small files), but that kind of sounds like he's talking out of his ass. Anyway, sooner or later everytime there's a problem I get something to work eventually. It's just a severe disincentive to perform maintenance I should be doing more regularly.
I'll try Kapersky's later. It can't hurt - what's one more BSOD? (Looked at TrendMicro, which I used to use years ago... wow has that place ever gotten TERRIBAD).