Replying to Computer Trouble.

So I've been away from home for about 2 days, and upon comming home I found that my PC does not want to start up when the power button is pressed. I played a few games / browsed the net for an hour or two before leaving and to my knowledge everything seemed to work perfectly fine.

I smell no burning electronics from the back of the case, but I have a feeling it is related to the power supply. Can anyone help me narrow down the culprits? And my computer was unplugged and turned off before I left so I'm positive no power surges knocked it out while I was away, nor anyone was there to fuck with it.

Thanks for reading.