No Mouse, No Sound, System Lockups?

I've been using windows vista 64-bit for a couple weeks now and, though I do find it fast and reliable, am having a huge problem -- the freaking OS seems to like locking up when it works with files of a big size (usually a few hundred MBs). It does not happen always, but pretty often -- to the point where now I save everything I have open before moving any file from a hard drive to the other or simply overwriting it. Its pretty annoying, it happens mainly with big files -- but has also happened a couple times with smaller ones, and I've noticed the pattern already - since every time it locks up like that the system is also doing some work in the hard drive. when it happens, all I can do i restart -

since the system dies completely, no mouse, no sound, no answer of any kind to anything I do but restarting and, once I do so, the system shows no signs of any error, so I can't diagnose whats happening in any way. Any ideas what might be happening? This is a high end system, so its not a lack of resources (amd 64bit dual core athlon 6000+, MSI K9A motherboard, video card is HIS RADEON HD 2900XT and hard drive is western digital 500GB, partitioned in two halves), and is honestly driving me crazy. Also sometimes it starts doing it at random, the system starts and about 2 minutes later it locks up with no reason -- and keeps on doing so several times..................