Double check they pluged the CPU fan header back onto the motherboard. Perhaps they completely forgot to plug in the fan. (lol, did it a few times myself).
Anyway, I'd double check with them and see what compound they've used, coz you do need some decent stuff nowadays, bog standard white silicon based TIM was good enough in the days of P1 MMX's, AMD K5's and Cyrix M2's, not for AMD FX70's Pentium 4 D's and the likes.