Do you have the original software? If so try Disk First Aid. It should say on the Original Disk what key to hold when starting up. Then see if that will fix the problem. Another thing to try: take the battery out of the Cube and leave it out for a while then put it back in. Reboot. I'm not real knowledgeable but it won't hurt to try these.Some have worked for me. Have you tryed zapping the P ram? Hold down Option, Control, P&R when you startup and let it ping three times.See if that fixes it. I hope you can get it going. Melvetta