Try cleaning the fan. First turn everything off.
Do not take your PSU apart.
Blow it, Suck it, brush it. The fan that is. Check that there is an easy supply of cool air to the cabinet. I have seen a PC installed in a Cupboard! My friend wanted to know why it kept crashing. Also pet hair and carpet fluff are killers.
This might not solve the problem, but it's free and it often does.