For unknown reasons, when starting up my G4 cube, the power light would light up, then go off. It did turn on but it would not function and then froze. When I got it back on a second time, it froze during doing apple disk first aid. Then I was unable to get the computer to chime. Now just the power light comes on and nothing happens...Could this be a power brick issue or some other issue on the cube? Where can I buy a power brick for the cube if that is the problem?