Out of my depth?

Just a wee bit.
Sitting at work today for some reason I remembered I still had a firewall that needed sorting kicking about in the garage.
So, boys in bed and after a bit of encouragement from my friend Google I thought I'd take a look inside to see why it wasn't powering up.
Google reckoned it was sure to be a loose connector where the power receptor joins the circuit board.
Sadly on this occasion Google was wrong :-(
It stopped working after a crazy electrical storm one night so it was highly unlikely to be a loose connector.
Hmm...nothing obvious, nothing smoking, nothing charred and voltage readings here and there but no power lamp!
Some bits feel warm but the heatsink on the processor is stone cold :-(
So that's that, I've reached the end of my capabilities @ resolving this problem.
Anyway, it was easier to reassemble than it was to take apart and I've only got 1 bit left over :-)
(oh yeah and it was very dusty in there!)