G5 Playing up

Hello all.
I am in need of advice please.
3 week ago I turned my g5 tower on and the mac didn't load up. My display came on and the round loading symbol just kept going round instead of of taking me to my desktop. As well as this the fans started and got louder by second, until they were going full speed.This happened for a few minutes until I pressed the restart switch and then it booted up fine.
Today the same thing happened again, it was after I put it to sleep. I tried to wake it by pressing some keys and this time the display remained on sleep and the fans started again like I mentioned before. After 2 minutes I had to press the restart switch. After that it loaded up fine. Does anyone know why this is happening? Any advice would be appreciated

Thanks:

Chris

what OS version is it running

Do you run any maintenance apps like MainMenu or Onyx

g5

I have just installed Leopard. I bought the machine 2 month ago, it cam ewith Tiger.Never had a problem with my old g4. This one is a the dual 1.8ghz. About 4 years old i think. 150gb HD and 1GB of memory. All I run is cs3.

Cheers

Chris

g5

I havnt heard of MainMenu or Onyx. Will these applications help?

Cheers

Chris

Surely will. Do a Google and download Onyx for maintaining scripts, emptying caches etc etc. Also Repair Permissions from time to time.