Shoutbox

My computer has been doing this for a while now, but it's never happened often enough for me to care about it too much. But since it's the holidays, i thought i'd try and do something about it.

When i turn on my pc for the first time in a while, it boots up and runs fine for a while but then one of the programs i have open (not necessarily the one i'm using) will lock up and become unresponsive. Then everything else will lock up and the computer becomes useless. My only option is to reboot.
Once i reboot, the computer tends to run smoothly and i have no other trouble with it normally.

In addition to that, sometimes if i leave the computer to go do something elsewhere, when i come back i'm faced with a BSOD (they have a range of error messages, and i can't reproduce them reliably to get them). But once again, after i reboot it's fine.

Like i said, it doesn't normally happen frequently, but earlier today when trying to copy about 110GB from one hard drive to another it crashed both times in the usual lock up fashion.

I'm currently running memtest on it to see if it's the RAM, but so far that's showing 0 errors (been running for 35mins).

So, after that lengthy post, any ideas?

EDIT: memtest finished; 2 passes, 0 errors. Ran HD Tune, no errors, SMART data fine for all drives.