serious boot problem

ok this isn't exactly windows 7 related but i need help anyway...

the last few days, when i hit the power button on my machine, it turns on but does not boot. i hear the fan on the psu, but nothing else kicks in.

after hitting the reset button a couple of times, then the boot sequence finally begins.

and here's the really weird part - it's happening at home and at work! well, it happened at work once yesterday. i suppose it could be a very strange cosmic coincidence...

what on earth is causing this?

Indicative of bad video card or bad RAM. In that order.

no, the computers are very different. nothing in common.

how can i troubleshoot this? why would bad components prevent the boot process form even starting?

How hot did the PCs get. You could have overheated them and caused some serious damage to the motherboard, it is a possibility. Before thinking that...remove the GPU and RAM and reinsert them, they may be loose or dirty for some reason. If this doesnt work then the GPU or RAM could be bad or the motherboard itself. Alot of things could be wrong in that situation.

my temps are ok, i keep an eye on them.

my home machine is a prebuilt and i have never opened it because i didn't want to break the seal which voids the warranty. i never really checked before but peering through the vents it looks to be incredibly dirty inside. i've only had the machine for many 9 months, but i have a cat, so lots of dust.

so now what? it's a half day journey on busses and trams to get to the place where i bought this. my wedding anniversary is this weekend, so i won't be able to take it in until next weekend at the earliest. should i open the case and clean it? i've been dying to get a new hard drive in there anyway.

in fact i don't even know when the warranty is up. i should check on that...

FullyLoadedMan - no other hardware. nothing.

no it stays in one place.

i guess i'll dig in there later and clean it out. i'm really amazed at how dirty it is. i'll reseat the ram/video card while i'm in there too.

any other suggestions?