Ah good work on finding the problem.
Does it actually respond or does it say that straight up? When its starting up tap [DEL] to enter the BIOS. Under PC Health Stats it should say the CPU temp, check if its too high like 60'C+.
Are you sure you mounted the HSF properly? If those i7s have the same push pins they can be a pain to get on. After 3 installs I still haven't got the hang of it
If the BIOS shows it too hot and the fans on properly then it might be a board problem. I saw someone fix this by flashing the BIOS to a newer version.