could very well be a HD going bad, I'm having a similar problem I ran the WD diag software and it claims the drive is fine, ran Spinrite 6 3 times, first time it seemed to find problems, I waited and waited it didn't advance at all in hours so I ran it again this time it reporting a cabling error not sure what that is? I ran it again switching the SATA cables on my 2 drives and both tested 100% the SMART checking utilities I've tried both report the drives are fine, but I'm almost 100% one isn't, PC was locking up and I had to reboot, since I've totally unhooked the drive I had 6 days of up time. BUt like I said every utility I ran (which was a lot) said the drive was normal, well except the one time I got the cabling error, which I can't find any info on what the hell it is.
I don't know if you have the means to back up your data, or if you even have data you care about backing up. But HD problems, or potential HD problems can be a damn nightmare to deal with. I'm on the road to buying an external to back my crap up once every few days, I'm so worried my 320 is dying I won't even hook it back up until I have the means to back it up.
I suggest you download Ultimate Boot CD, run memtest86 if you haven't - let it run overnight to make sure your memory ain't the issue. Run the DIAG program from your HD makers, but don't take what it says as an absolute if it says "drive is fine" if it reports SMART errors RMA that sucker asap. I guess all HD's fail sooner or later, sometimes we get lucky and get warning enough to get our data safe before it totally takes a dump.
good luck let me know if you figure out what it is, maybe I can get some ideas from you about my own HD problems
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