Same boat. My PC worked fine then after switching it off it just wouldn't restart at all. Nothing. I had a light on the GPU but nothing else.

 

A bit of playing and it turned out to be the PSU. Corsair V1200. Replaced under warranty and first message I got was the overclock failed one.

 

I'll check my pump and re-do the heatsink paste and see how it goes.

Could well have been just the PSU that failed. Doesn't take much to confuse the UEFI and generate the "overclock failed" massage. You may have no more issues.

 

However, an example of how insidious motherboard failures can be...

 

 

A while ago, crackling noise form the wall socket, ignored it at first until it became more frequent.

 

As I'm handy with electrics, I changed the 13 amp wall socket.

 

Intermittent crackling from the socket once every 3 weeks or so continued, so changed the 13 amp socket again.

 

Crackling from socket again. This time it blew my PSU and surge protector. tested the PSU and dead, so got a new one under the warranty and bought a new surge protector. That should be it I thought, problem solved. Boy was I wrong.

 

More crackling from the socket on turning on the PC. New it couldn't be the wall socket, PSU was new, surge protector was new. So I thought sod it, and bought a new motherboard and PSU.

 

Problem solved. All that time it was a faulty motherboard.

I took my PC to NCIX this week and I was told after a few days of testing and switching out hardware that my CPU is buggered.  I'm going to try to replace the CPU with a used one so I can systematically uninstall FSX and P3D and all addons and plan on building a new PC.