Pc boots up for a few seconds and shuts off again

[bugeyez]

So about a year ago I built my first gaming PC, ever since a few months ago it was working fine. I did have a ram issue but got them replaced. Now I have another problem, my PC will start up for a few seconds and shut off again, it can't get past the self boot up. I've tried booting it with just the bare bones. As well as using 1 ram stick then the other and then with both. I've removed the mobo battery, replaced motherboards and yet still Nothing seems to be working and I'm not sure what to do ):

 

[R4lNM4N]

Sounds like it's hot. Re-install the CPU cooler/ensure the fan is working.

 

[bugeyez]

The Fan works fine and I've reinstalled it twice now, I have 3 other fans in my pc so my pc is usually very cool.

 

[R4lNM4N]

Too much thermal paste will insulate the chip

 

[R4lNM4N]

It would also be helpful to list full system specs. And explain the RAM issue - was it corrected? As in, you swapped the RAM, it worked fine for an amount of time, now this new issue is not at all related?

 

[Rumbletum]

Power supply issue?