Power Mac g5 issue

I'm confused by a lot of posts on google Ect.. So I'm wondering if anyone on here can assist. I build Pc's for a living and my knowledge of apple macs is limited if not nothing. Apple powermac g5 dual processor 2.0. Can't get it to boot from install disc.. Tried various memory arrangements knowing that it should be on pairs from the middle out. Change graphics card and various harddrives. Problem I get is I get to the mac os x disc with the arrow pointing to continue and the apple logo appears and the whirly loading icon and it just stops on that.. If left for longer than 6 mins the fans go full blast. By looking online apparently according to apple by typing in the serial number it uses leopard??? I have tried that and a lot of other ones. Some with the mo entry sign some with the apple logo then it goes offset on the screen as if it's crashed. The only slight progress is with the leopard disc. I have..... Stripped the machine changed DVD rw... Removed power supplyand checked for bad caps.. It like new. Changed the CMOS battery. Cleared nv ram. Pr . And set to defaults . I've spent many hours on this and it's driving me nuts! I get the chimes at start up everytime and a display. Any help would be great thank you in advance

I suspect that the logic board could be kaputt (technical term). Sadly they are a little prone to it.
This would explain the fans.
I assume the Leopard disc you are using is the generic black disc, and not a a machine specific grey disc.

Okay, I know this answer may seem overly simple, but after working in Geek Squad for a few years, you have to ask ALL the questions...

You are holding down the "C" key upon boot, correct?