A few months ago I got an oldish PC that I wanted the CPU out of, took it and the motherboard out, tested it, worked fine. Had a look at the CPU temps and they would fluctuate quickly from 37-39-40 and would do weird things like that. Try and run a game or anything and temps would go to 78 very quickly. The CPU in question is a Intel I5-2400. I got a new motherboard and a new CPU cooler and still have the same results. Whats going on?!