PowerMac G4 MDD Boot Cycle D:

So I have this 2002 PowerMac G4 MDD dual 1.33GHz that refuses to boot sometimes, and I cannot figure out why!

I just replaced the power supply, though Im not 100% positive that this new one is in perfect condition. I have to check the volts later.

I currently have a 80GB drive with 10.5.8 in it and sometimes it boots, other times I get the screen with the apple logo on it, then black screen, then it does one of two things. It either repeats and goes to the logo then black screen, then logo then black screen forever, OR it goes from the apple logo to a black screen and stays black and I can hear it doing something inside. Apperantly the speaker is broke and when I plug in headphones I hear the startup chime over and over and over with about 6 seconds between them EVERY time. Why?

I have tried using a different GPU, no effect. Booting from 10.4 CD or DVD, or 10.5 DVD, no effect. Still Apple logo then black screen. I took out the battery and hit the little button on the motherboard when it was unplugged and that didnt help. I can feel the heatsink and its hardly even warm at all, so not overheating...

Does anyone have any solutions? Im about to pull my hair out! I'd love to get this back in everyday usable condition, not just "once in a while" working machine!

Thanks in advance guys! If you need any more info on this machine, Id be happy to provide it, along with pics~