Britton30 said:
Less isn't really more but the proper amount IS needed, than being a drop of material about the size of a grain of rice in the center of a thoroughly clean CPU, only on the CPU. The heatsink mating surface should be equally cleaned then tightened down evenly.

I would make a guess and say you've likely damaged the CPU when you had the heatsink mounted wrong by overheating it. What new cooler did you get?

This free program will monitor and show your PSU voltages. HWiNFO, HWiNFO32 & HWiNFO64 - Hardware Information and Analysis Tools
I would try this first to see if the PSU if faulty.