Just spent 3 days working on a machine.
These are the symptoms it had:
When power was turned on, all fans spun up, hard drives clicked etc. Nothing else happened, no beeps and hd led stays on.
Spend three - thats THREE days trying to sus this out, pulled all cards, drives etc. Tried new ram and gfx card, pulled mobo out and looked forany dry joints/cracks.
Just when I was about to bin it, I fired it up one more time, and for some reason tried to press the reset button. it didn't move. pulled reset wire off mobo, fired up and into OS first time.
The front of the case is bashed in from a previous (seemingly) 'unsolveable' problem, and the button got stuck, popped it out and it all runs fine.
I feel such a fool.