Fan Speed at full

I have a G5. it give this message on Single user mode. "power management received emergency overtemp" and the it shutdown. I havent be able to boot into the OS. I got this computer from a friend without a video card, I havea g4 and I installed the g4 video card into the g5 (ATY Rage pro 128) can that be the issue? I also had to replace the Liquid Cooling System and CPU board because the seals were bad and leaking. power supply, motherboard and case have no sing of liquid damage. (Excuse my english, I still learning) Thanks