Mac Won't Start Up (Cuts Off)

Hey everyone. Newbie here.

We have a G4 iMac with a 17" flat screen. With OS 10.4 installed. The problem is, it won't start up. When the power goes on, it comes up a grey screen, then just cuts off. Like there is a power cut; it just switches off on its own.

Beforehand when it was working, we were running Disk Utility through it, and we had to force it to quit. It mentioned that it could damage the disk if we did a force quit on it. But we quit anyway.

We can't seem to work out the problem. Whether its a hardware problem or a software problem. We tried PRAM and everything, but no luck. Maybe it was that Disk Utility that caused the problem, but we need to know what it could be and how to resolve it.

Any help appreciated.

Not good news for the HDD.

Can you boot from the Tiger install DVD? If so go to Utilities and run Repair Disk from there. After that a job for DiskWarrior if you have it, or a new HDD.

Did Disk Utility have a SMART warning did you note?

I have the same iMac. You should have the Apple Hardware test cd. If you're still having problems after harryb2448's suggestion, give it a try.