Why wont my Kaspersky 2011 ever finish scanning 100%?

I have the Kaspersky 2011 program on my computer, and I scan my computer every week to be on the safe side. I never visit sites or download untrusted or suspicious files onto my computer either. Until several days ago when the scanning process began to act a little funny; it would never finish scanning! At first I thought it was just a slow day, but after I left it alone I came back and it said it'll take 3 weeks to finish! I thought it was a corrupt file but the scan never "froze" on the same file, but it did in fact always freeze on 72% completion (then it just takes an eternity). I don't know what is wrong and I think it could be the work of a virus that doesn't want me to finish scanning. But like I said, I don't do anything on this computer that will cause any harm whatsoever, though I believe that this has do do with an outside force that is impeding my computer's capabilities. Please help! (I'd hate the idea of losing this computer)