Cube G4-500 here. I cannot get it to boot at all. I get the gray screen with flashing folder/question mark/face. I tried to boot from the HDD, CD, and using target disk mode. Nothing can get me out of this, and I know the HDD is good because I pulled it out and re-imaged it on another machine just fine. The power button on the cube and studio display shut the machine off and turn it on just fine. I am perplexed.