I doubt that you'll fry them if you had a good hsf on it. How did you manage to fry 2 of them?
Anyways, keep the case open and look for problems. If it starts up, posts, then shuts off randomly afterward, then you have a cooling problem. Oh yeah, make sure your hsf is plugged in!! Thermal greese helps, but your cpu shouldn't have fried without it, unless you got some 1 dollar fan that didn't run.