Greetings,
So the PC will not power on and shows no signs of activity whatsoever? No LED's, fan movement, nothing?
I didn't realize that. I though after you unplugged it that it started, but failed to boot.
If that's the case, it seems like something else might have happened while you were away.
Try removing power to the motherboard and removing the CMOS battery. Press and hold the power button the case for 30 sec. Now reinstall the battery and reconnect power. See if it will start.
If not, leave power connected and short the CLR_CMOS pins 10-15 sec. Some boards have a button.... if this doesn't help, you will need to bench test. You will need to test the PSU first. If you have a spare, use it to test power.
Start removing any installed add on cards, etc. Continue testing. If you don't have these components to test with you may need to take the system to a repair shop for validation.