Powermac G5 Won't Boot

Hello there. myself being an Apple tech enthusiast and a wide knowledge in macs I have a problem that I have been unable to solve my self. I have a Powermac G5 running Leopard, and when I push the power button i see the apple logo and spinny ring as normal mac boot up then it goes to a white screen then flashes and goes to another white screen then just stays there :/

I have done traget disc mode to it from my mac pro to verify/repair the disc but it says there are no erros on the hard drive. Please could someone help me ASAP

Many thanks