Need Help Diagnosing Hardware Issue

My main desktop PC seems to have some problem that popped up randomly. I’ve ruled out software, but haven’t entirely ruled out the system hard drive (as it’s from a server from a buddy’s workplace, so it may have been used for years before I got ahold of it, but a 17gb SCSI Ultra160 hard drive isn’t cheap to replace).

I’ve been told to reseat the CPU and RAM, strip it down to bare bones, turn memory check on, and build it up from there, to help pinpoint the problem. Such a time consuming task, but there’s probably not much else a computer repair shop would do for me anyway - so I’ve ruled out bringing it somewhere for them to have a stab at it.

The problem: Even after a SCSI format, and then a format of the drive while installing Windows, the computer will freeze during various tasks. Seems like it’s having trouble either accessing memory or with some particular CPU function(s). I don’t notice any hard drive issues, but as I said, I won’t rule that out just yet.

Anyone have any other ideas?