We will never know, but I wonder if it could be a power/signaling or VRM issue - the CPU non getting hot doesn't mean something else on the board has gone out of spec and into catastrophic failure.

Motherboard issues around power/signaling are a pain to diagnose, they will emerge as all sort of problems apparently related to other components (ram failing to initialize and random restarts are very common in my experience) and you end up swapping everything before actually replacing the MB...