Friends computer doesn't make a sounds

[JAGedlion]

I built a computer for a friends a couple years ago and recently he decided to rearrage the mess of cables comming out the back.
Now, I've always thought that nothing really bad could come about because of such actions but then again he also said he "cleaned some dust from the inside" though with only a paper towel.
Either way, the computer now no longer boots, like, you press the button and nothing, no fans, no beeps, are emenated, even when I had him just unplug everything but the power from the computer.

I am planning on having him check the power button's connection to the mobo and reset the CMOS (don't worry, I made sure the PS was switched on), but considering his relative incompetence with computers this will already be a rather painful procedure and as such I wanted some other advice so that I can get it all fixed asap in as few calls as possible.

 

[mechBgon]

What motherboard does it have? The most likely explaination is that he pulled the case's power-button wire off the mobo while wiping out the dust bunnies in the bottom of the case. If you remember the motherboard, I may have the manual and be able to do one of these for you to send to him.