Computer problems

Dumb computer! The other day it started shutting down on its own after being on only a minute or two. Ok, so it's either the power supply or a heat problem. Put on another power supply. Same problem. Check the heat sink, Jerry! Check the heat sink! Oh, what do I see, but the bracket on the motherboard snapped off, so the heat sink/fan is not tight up against the processor. Excellent! Took it to a guy who rigged up something to make it tight again. Take it home, hook it up, heats up, shuts down. Huh? What gives? Call the guy back... "Hey, heat problem still a problem." He say, "no problem, 70 degrees is not hot, change your BIOS to keep computer from shutting off." Problem: 70 degrees (celsius) IS HOT! Let's see, divide by 12, add 32, and reverse it... about 153 degrees foreign-height!!! Check BIOS, only lets me choose "shut off at 50 degrees" or "Shut off at 60 degrees" or "Shut off at 70 degrees" or "don't shut off." So, just for kicks and giggles, I picked "don't shut off" and guess what? It didn't shut off. But according to Mobo monitor, I'm running hot hot hot. Touch the heat sink, feels cold cold cold. I'm thinking maybe I need to get some heatsink adhesive or sumptin, and stick that bad boy on firm and tight. But honestly, I don't know what I'm doing. Figures... this happens on the VERY NEXT DAY AFTER DISMANTALING MY SPARE COMPUTER! Calling on Calculus!