My iMac G5 1.6 Ghz Won't Boot. Shuts Down at Gray Screen. HELP!

Hi guys. I need some help. I have an iMac G5 that seems to be having some serious problems. It is a 17" 1.6 Ghz w/ 1GB of RAM.

The problem:
• When I press the power button, I get the beautiful Mac chime, and the LCD turns on to the gray apple screen. I get the spinning gray bars below the apple, and then...it shuts down. Sometimes it doesn't even make it to the gray screen and it shuts down.

What I have done recently/tried.
• I installed iLife '06 and all the updates a day or two before this began.
• I reset the PRAM.
• I tried booting in safe-mode...no luck.
• I tried starting from the factory CD. The drive begins to spin, and then it shuts down.

When this first happened (yesterday), I started it in safe-mode, and everything looked ok. I zapped the PRAM, and then started it up, and once again, everything looked ok. That was last night. When I got home from work tonight, none of those things worked, and I am now looking for some help from you guys. Any suggestions? Thanks, in advance, for the help.

BTW, I think I'm running 10.4, but I'm not certain because I can't start it up to tell.

UPDATE:
I also just tried resetting the SMU. I got past the gray screen to the blue screen, and then WHAMO - it shut down. That's the farthest it's gotten today, though. Any ideas? Thanks again, AC.

Did you find a way to solve this problem. Because I have the exact same problem with my iMac G5 20" today...

Hello to both of you and welcome.

Check out the links in this post, it might help both of you.

I had this problem with my iMac G5. Let me say this, i hope you have a warranty. I took mine to the dealership and it was under warranty (thank god) because they replaced the logic board.