Your machine is old enough to start experiencing failing hardware, especially if it's been heavily used.
Anyhow since you bring up a possible ram issue.
It may be the ram itself and not the slot that is bad, ...or it could be the slot
Running this overnight (5 to 7 passes) will detect bad memory for you. Though if it's as bad as it sounds I'm pretty sure you'll start getting errors almost right away if memory is the culprit. (it really should be run for half a dozen passes or so to be safe though)
edit: oops forgot the link
RAM - Test with Memtest86+