InvalidError :
A power line surge when the power cut off or came back may have fried the PSU. I've lost one PSU and two CRTs to bad power in the past.
This is pretty much what I think it is as well: You lost power and it fried the PSU when the power went back on after the power loss.
If unplugging the cord and allowing the computer to sit totally unplugged for a few minutes does not fix it, I am almost certain that is your issue: Power supply blew.
It is not all that expensive to get a power supply replaced in a desktop PC today so you might want to head to your local computer repair store and have them replace it.