I have a 17" G5 (early model). recently the computer is having starting problems. Often I just get a black screen and the fan speeds up. Sometimes the computer actually runs ok for short while, then freezes. Reboot results in blank screen. The computer also does not accept a boot disk in the slot drive most times. I have swapped the internal drive and also swapped out the ram sticks, so the problem isn't there. I have tried booting from an external drive, I have reset the pram and any other system reset I can think of. I have also tried a different keyboard. Whatever I do the computer usually doesn't work, although occasionally it runs for a while. Computer spec: 17" iMac G5. 1.6ghz. OSX 10.4 256 mb ram.