Relax, this is a common issue
Your power supply has gone dead, and needs to be replaced. This is not a horribly expensive part, however, if you are not the best with computers, I suggest having a professional install it for you. Take the computer to your local computer store. They will tell you which power supply you have, as well as which you can buy to replace it. Buy the supply, and have them install it for you. I say this because if you are new to the whole thing, it can be dangerous handling such a powerful unit.
Flame