My desktop G4 has been working great for years. I recently powered down, then when I powered up, fans turn on, I get the chimes, the grey apple screen, the spinning wheel, then, a minute later, the fans turn off and the whole thing powers down. With a safe boot, it has the black screen with white lettering and says several things like (forgive me for not being exact - it happens fast) "can't complete .... " and has a few screens of this, then pauses, then says "killing all processes" "cpu done" and powers down again. I've tried booting from the install disk, and it powers down again. I've removed all peripherals, including extra memory and extra usb ports, same thing. I've plugged into different outlets, same thing. I've reset the little PMU switch, same thing. The little battery measures 3.6V. Any advice would be appreciated.