Is your CPU or your GPU overclocked? I beleive this sounds like an unstable overclock that hangs the OS on high loads. If anything at all onboard your system is overclocked, I would suggest downclocking right now and testing your stuff. Also, check to make sure your CPU heatsink is seated properly and has a nice and reasonable coat of thermal compound, as your CPU could POSSIBLY be locking up due to high temps. On a less likely note, check for viruses, and uhh, maybe give your storage volumes a good defragmenting. Severe fragmentation can cause problems like this, but as I said before your not likely running on a REALLY REALLY fragmented system.