G4 FW800 wont boot anymore

My FW800 had a broken CPU. The guy who owned it before soldered there something and after that it booted until the apple logo and hanged after that. Now i got a new cpu from a MDD (both are 1,25Ghz CPU's). I installed it but it didnt turn on. The computer started, but after a while the case fan started to blow very fast and nothin else hapend. I removed the CPU and noticed that one pin was a bit moved sideways( i'm not sure if it short-circuated something, could be possible). I bend it straight again and installed the CPU back. Still the same problem.

Somehow i noticed the PMU switch, while the computer was running i pressed it. Still nothing. I'm pretty sure i pressed it twice after the computer shut down. Still the same. Also noticed that the power button lights up for a second when i press it, the computer starts but the light goes off. So i did the PMU reset the way it was ment to be. Removed the power cable and the battery and pressed it once. Still the same problem.

I tried my old CPU but the same hapend with that.

So what would you guess, did i brick mu motherboard, and possibly my new CPU too? What should i do and how can i be sure what works and what not.

Oh and i measured the voltage of the battery, it was under 1V.

Just in case, my old CPU had a sticker on it:KC3090HKP6SA* SINGAPORE MPU 1.25 GHZ DP
My new one has:J53325NGPXAA* 630T4800/630-4799 CN MPU 1.25GHZ

Could it short-circuated something on the motherboard or are the pins just sensitiv and need a real good grip?

What about CPU's from different revisions, can they be swapped?

Ill try inserting it again, and removing memory and graphic card. But something tells me it isn't that. I think i should look for a new motherboard

EDIT: So i tried everything. Run it without a graphic card and ram. Nothing happend, still the same. It goes on, the power button glows for a moment and afer ~15s the case fan goes full speed.

So what are the possible causes:
1. The motherboard is dead?
2. Both CPU's are dead (the old one is for sure, i forgot the heatsink and started the computer, it was running about 20s and i guess that was enough)?
3. The new CPU doesn't fit in my FW800?

I'll try to find someone with the same computer and try the cpu. My guess would be the motherboard, but, it could be both the motherboard and the CPU.

Yeah but i got a new one from ebay. The seller tested it and it worked.
I tried without the CPU and then the computer doesn't torn on at all. Only the power button flasher for a moment. But in my case the fans start spinning.

but maybe your right, i should go to a dealer or something.

Nope, never figured it out. I went to a local Apple store and they sayd that the CPU probrably took down also the motherboard. But i wasnt able to test it and sold the machine for parts.