It's more likely that your MB is shutting down PSU, not the other way around. Double and triple check cooler mounting, specially back plate, that's only place you can get a short. If it's Intel, check for excessive cooler pressure on the processor. It can also bend even AMD based MB if cooler is mounted with improper spacers and is too tight.
Try with standard cooler if you still have it.
Thanks a ton for the answer. I am nearly certain you are correct. I did indeed mount my cooler and screw it in with a lot of pressure. I will correct this immediately.