Computer shuts down?
It most probably is the CPU temps in the 1st case and PSU in the 2nd IMO.
1. If it's shutting down and not re-booting, it prolly is the temp. Is 46 degrees on load or idle?
2. Try monitoring the voltages with Hardware Monitor
and post back.
3. Try testing your memory the way I mentioned in my last post.
If you get nothing, then see if somebody will lend you a working PSU for a day and see if that takes care of the problem.
If even that doesn't sort things out, the Motherboard's gotta go, I think. But first things fist, start with step 1 for now.