I have a Windows Home Server that I built using a barebones Shuttle KPC. It was working great until yesterday. It won't power on. The fans don't spin. And obviously it doesn't boot. I suspect the power supply bit the dust. However... the power indicator light on the motherboard lights up.
I have had a similar problem on occasion with a different system, and I think mine is caused by temporary confusion in the BIOS. My solution is to unplug from the wall (or just reach around the back and turn off the switch on the PSU) and leave it with no power for at least a minute, maybe 2 or 3. Then reconnect power and try the front panel button. For my system, that completely cold re-start works.