+1 on the problem probably being Kaspersky; we had been using Kasperky at work for almost a year when suddenly PCs started freezing randomly and requiring a hard-reset to get out of it.  After about 2 man-days of investigative effort someone decided to uninstall Kaspersky from their machine and the problem immediately went away. There had been a Kaspersky update which just killed machines.  Luckily we were only a couple of weeks from our licence renewal, so we're not going to waste any more money on them.

Herbie