Thanks so far guys. I need all the info i can get. Its my Teacher computer and she is trying to get it running again (she does have a MacBook). But it was a Expensive machine and she does not want it dieing.. Give me all the info you got thanks!
If it's a coolant leak, you're in luck. I wasn't using my G5 a whole lot anymore, and then one day I turned it on and the screen wouldn't turn on. Chimed up, drives spinning, but nothing else. Opened the case up and noticed some fuzzy orange/brown gunk under the processors. Panicked, quickly google'd 'G5 coolant leak'. Found its a rather common problem. A call to AppleCare and they were setting up an appointment for a local genius.
They said the repair would be free. Logic board, power supply and CPUs (dual 2.7 model). I was ok with that.
New parts came in, still wouldn't boot, so they're replacing it with a Mac Pro of similar specs.
Keep in mind the Dual 2.7 G5 was top of the line in it's time. I had the GeForce 6800 Ultra, Airport/Bluetooth and 8GB RAM (upgraded via third party over the years).
They're replacing it with a top end Mac Pro. Supposed to be getting a stock 8-core 2.93 GHz, 8GB RAM, Airport and Radeon 4870. Should be in, in 2-3 weeks. Guess that's when I find out if I'll get what was said over the phone.