|chkdsk -r -f -x|
^ to check your hard drive for bad sectors and mark them unusable (will run after reboot).
Your symptoms sound RAM related though, is it the same RAM you've always had? If it's new, put the old stuff back in. If it's the same stuff you've always had, try popping it back out and re-inserting it ("reseating" the RAM). This might help if the ram has started to "creep" up out of its slot.
if that doesn't help, i would download and run memtest86 on one stick of RAM at a time. write to a floppy or CD/DVD and boot to the disk to run memtest, it will stress your RAM and report any errors it finds. if one stick has errors, remove it and only game on the other stick. if they both have errors, time to replace the ram.