2005 2.7 ghz PowerPC G5 won't boot up.

We have a 2005 2.7 ghz PowerMac G5 that has been working relatively fine for the three years that we've owned it. We do not seem to have the original OSX disks. I have tried literally everything I can think of and none of the suggestions online seem to work. The first issue it started having is it would reorganize the desktop whenever it was shut down, even though auto sort is turned off. So we would just put it to sleep at night instead of shutting it down. Then it started running horribly slow and the rainbow spinner would spin all the time. It only has 2.5gb of ram in it so I thought maybe it needed a memory boost. I purchased 4gbs from Corsair and thought the speeds matched since I checked one of the 1gb chips that are in it. Turns out, it's been running with 2gbs of 3200 and 512mbs of 3200u. I heard this can created problems. Anyway, the new corsair memory is 3200. I installed it and booted the computer up. It came on fine and it seemed a little faster. I shut it down to see if the desktop would still get rearranged and the computer hasn't come back on since. At first it would just at the grey screen and the spinning indicator spun for 4+ hours. I removed all of the memory except for the original 512mb. And that didn't do anything. I tried running fsck -fy in single user mode and that seemed to run but would then have an error at the end and it didn't actually seem to do anything. I tried resetting the PRAM, NVRAM, tried running it without any peripherals plugged in, tried resetting the pram by pressing the button on the logic board, everything that is generally suggested, I have done. Now the computer won't boot at all. It turns on, gets to the grey screen, then crashes and shuts off. I've tried verbose mode but I don't get anywhere because it crashes. It also won't boot in safe mode, just crashes at grey screen again there. I tried running a few diskutil things from single-user mode but they all say "cannot be performed because it's in write mode" or something. It won't let me mount the device or run fsck anymore because of some B-Key errors. I am completely at a loss as to what the problem could be. I also replaced the logic board just last night, and while it gets further in the startup process than it did, that doesn't appear to have been the problem. The latest thing I came accross suggested that after trying all this, it could be some messed up permissions or disk key errors or something in the hard drive, so I have Disk Warrior on the way in the mail. I'm just worried this won't work either and then I really won't know what to try next. Anyone have any ideas or suggestions? I almost feel like it's something easy / silly that just needs to be fixed but I don't know how to do it... I can actually post my error messages too if that helps. From single user mode and what not.

Thanks