Ok, now I got a P45 motherboard and tried to boot up all my existing stuff in it but it kept just turning off and rebooting. I set everything up outside the case as I ordered a new case from Scan and it's due to arrive tomorrow so I thought I might as well set it up outside the case. I "turned on" the motherboard by shorting the power pins.
So then I put it back in my P35 motherboard did exactly the same thing and it repeated the restarting. So I finally decided I'd screw it back into the case and plug in the headers and such and now I still get the same problem. Searched it up on google a bit and took the RAM, GFX card out.
I have narrowed it down to the CPU, PSU and motherboard only and it comes up with the post codes 8.3. to 9.0 to 9.8 to 9.9 as far as I can see.
According to the manual this means:
8.3. - ATX power supply ready
9.0. - AWARDBIOS take over booting job
9.8. - De-assert ATX power supply
9.9. - Complete power off sequence
Sigh so many problems today, doesn't help that I can't even boot up my own pc...
EDIT: I have tried clearing the BIOS of both boards multiple times.
Gonna try another power supply but it only has a 4 pin connector... Might be a bit risky. Haven't got any other 775 CPUs to try though.