Imac G5: hard drive failure or worse....

When you open 'her' up look at the caps that G5 may have been built when a lot venders bought cheap electrolyte http://en.wikipedia.org/wiki/Capacitor_plague  a lot of companies beside Apple got hit.

We had one board in the church rectory get hit and I could not find an identical board but found an upgraded one with the same chip sets and windows never knew it was swapped out. I was very lucky; that one finally got replaced with an iMac intel.

Good luck, if have not taken it apart ifixit has some good text and images and if you are in there blow out the dust bunnies and I am sure that is a SATA drive you probably can replace and breath new life in to it.

Ciao,

Lou Cioccio