quad G5 won't boot up: fans are going full-blast?

[chimpanzee]

I tried to boot up my quad G5 in a really hot room, & I got an error message:

"power down the machine"

I depressed the power button to power-down the machine, but when I tried powering back up it wouldn't boot up. The fans started going full-blast.

I tried the command-option-P-R, option, shift keys depressed during power-up..no go. I also noticed my keyboard wasn't getting any power (pressing the shift-key doesn't light up the shift light).

I tried the SMU reset according to:

http://docs.info.apple.com/article.html?artnum=300341

I was able to boot up the computer, but shortly thereafter I got the same error message above ("power down the machine"). When I tried to boot up, I got the same old problem: empty screen, fans going full-blast, keyboard not on. I reset the SMU again, but this time I wasn't able to get a successful boot..same problem: empty screen, fans going full-blast.

What's going on? How do I fix this problem, I need to use my machine..

Recently, I would get intermittent issues with the fans going full-blast & I would have to power down the machine. It would always boot back up OK, though.

Is this a software issue with a bad release of OS X? (fans going nuts, I heard some complaints on other threads about it)

[Satcomer]

Call AppleCare and hope you have a backup because you are having a serious hardware problem.

[MacGizmo]

Well first of all you need to get the machine out of the "hot room." The G5 runs extremely hot on its own, and the sensors are extremely sensitive. Once you do that, turn it off and let it cool down. Then, start up from the install CD by holding the C key down (if you can't get the Mac to start up properly, try holding the mouse button down while starting up which will eject the DVD tray, then put the CD in and restart holding C).

If you can then get the machine to boot from the startup DVD, run the DiskUtility application and repair the drive and permissions.

If this doesn't solve the problem, AppleCare WILL tell you to run the TEST CD that came with the machine. It takes a long time (hours depending on HD size and amount of RAM) and will most likely tell you the machine is fine. Then you can take the machine back to an Apple Store and have them replace the sensors. And when that doesn't work they'll tell you that one of the processors is bad. And when they replace it and it still doesn't work, you take it back again and they replace the motherboard. When that doesn't work, you take it back yet again and they just take your hard drive out and put it in a whole new machine.

Gee, it sounds like I've gone through this before, doesn't it.