PC issues

[Tatsuki]

I have a PC that I can't figure out what the issue is. Its a LG115 era i3, that won't boot.

I left it for a month and it worked again for a month. Then this week it won't boot again. Same symptoms as last time I turn it on and fans spin hard drive spins, no beeps, but nothing on screen (Keyboard does not light up on boot) I left off over weekend it booted once then fails to boot again now.

I stripped everything out, reseated CPU, unplugged ram, changed power supply, tried booting with only CPU and one ram stick, nothing works. The only thing that seems to do anything is to leave it totally off for a random period of time and magically it works again for a random time then fails again.

Really lost on whats wrong, Thinking it's either the CPU or the MB but I don't have a LG115 MB or processor to test them against.
Any ideas?

 

[Tatsuki]

Thanks for the answers, it's using onboard graphics, I did try VGA card and that didn't work.
I think it might be a short somewhere too, but why it seems to spring back into life when left for a while is a bit confusing if it's a short? I have motherboard out of case on a antistatic mat at the moment so can't be case?

I don't think Overclockers stock LG115 motherboards anymore?