PC Keeps turning on and off repeatedly (maybe overheating?)

[chimichanga3000]

I build my pc nearly 2 years ago, and its been perfect until last week, everytime I try turn it on, it keeps turning on and off by itself. I unplugged everything from the motherboard, and it still did this. So I think its either the motherboard (Asus z97 pro-gamer) or my psu (thermaltake Smart SE 630W. I don't think its the cpu.

But is there anyway I can known for sure? I don't have a lot of money right now, so I don't want to buy the wrong thing haha. Many thanks though!

 

[cin19]

Clear the CMOS first by the jumper. May test the PSU by paper clip method http://forum.corsair.com/v3/showthread.php?t=63991 even try other PSU if you have other one.

Disconnect the HDD/SSD, also unplug the RAM too, using onboard iGPU to boot the PC. Can you boot it ?
1) If you can boot the PC, but get the no RAM, no boot device. That means the PC is fine. And add one stick memory if you have more than one, then boot the PC. If it will boot then add back the hardware one by one.
2) If the PC will not boot at all. Test the cpu or MB, but the problem may from the MB in most time.