Stuck on Apple loading screen with the fans running at full speed

Hi Guys

I recently installed new ram into my power mac G5 and it is having trouble booting up. After installation it booted up fine but the ram had not registered on the computer. I moved the cards around following all the correct RAM procedures (installing in pairs, working from the inside out, etc) I got to log in and it was on maybe 3-4 mins before I got a panic kernal(fans started to speed up to the jet engine stage) telling me to shut down the computer and I did. Now I am unable to log back in. It stays on the apple loading screen with the rotating gear. After 3-4 mins, the fan inside the computer starts to speed up to a very high speed and I turn the computer off for fear of breaking the computer. I have tried Safe Boot but I cannot get passed the loading screen. I reset the PRAM but to no use. I tried the sbin/fsck-fy command but it was telling me that the command was an invalid length. Your help on this matter would be great!