IT Was working fine before you left for work..
Do you have kids or elves that run through your house to mess around with your computer?
Ok Think logically. Right now the power is flowing from the wall to the PS to the Mobo and you can see the light on the mobo?
That doesnt mean that the PS is fully functioning to get the charge directly to the Mobo/VID/CD/SATA/Fans.
You could have had a resister in the PS just fault and basically say thats it I am tired. It happens. If you have another system just to test it on or a friends computer to test it on.. Return it to wherever you got it. Get another 1 trial 1 over.. No need of pulling apart your CPU cooler or any other junk like that.