Power/booting probelm please help.

[Phill84]

I've had my acer for a few years now. Origanly the problem was, it would just turn itself off with no warning. Then it started having problems booting. I'd press the power button (which lights up as well as the led's for power supply/batt charging) and before the acer screen would normaly display it would turn itself back off (baring in mind laptops cold).
I found that if i kept trying it sometimes after 3rd time or times 20th time it would boot and stay on fine.
I thought it might be an adaptor problem or battery (battery didnt seem to be holding the charge, I found i had 2 keep it plugged in). AC adaptors ok and I replaced the battery to see if that was the problem. The new battery held the charge and was charging ok but still had the problem (which by now it was proggressivly getting more often).
I'm now at the stage where it won't boot up no matter how many times I try. I've checked my RAM in another laptop and there fine they work in another laptop and probem is still there when i swapped.
So I lnow its not the screen as I've seen this working even if its for only secs before it turns itself off, so now im thinking poss power unit on the motherboard.
How can i check/find this before I dismantle it or any other suggestions or tests I can try beforehand??
Thanks Phill

 

[Prostar Computer]

Based off the timeline, it sounds like either heat damage, or electrical failure (seems more like the latter). If that be the case, you'll probably need to replace the main board.