Trobleshooting restart

I have a couple of users here how are complaining that after there computer starts up, that alot of the time it automatically restarts. Could anybody help tell me a good way of trying to locate the source of this problem. I’ve read in other posts that it could be a hardware issue, but the harware on those pc’s is the same as everyone else’s, but they would use a little extra software that is memory/processor heavy.