So yesterday I came home from work and went to turn my computer on....it turned on for about 5 seconds then promptly turned right back off again...before I ever saw anything on the screen. I tried again, same result.

After several attempts, I've found that the length at which it turns on differs. After trying multiple times in a row, it only stays on for about 3 seconds. If I let it rest for a bit it sometimes will stay on for up to a minute (though it never boots, the screen stays black the whole time).

I'm not sure what is causing this issue...I built this computer a little more than 2 years ago and this is the first issue I have ever had with it. I did all the usual checks:
-It's not the power switch
-The capacitors on the motherboard all seem to be in working order
-The PSU seems to be fine as it lights up, fan spins, and will sometimes stay on for about a minute period

My hope is that the thermal paste on the cpu has degraded and just needs to be re-applied. Does that seem like a reasonable assumption?

I'm going to tear the thing apart and do a minimum system build when I get home, but any heads up as to what I should be looking for would be much appreciated.

Any thoughts?