Reboot hell on Giga P31- DS3L

I have just built my system comprising of giga P31-ds3l, E2180 and crucial ballistix. It built the system out the case and used my HD3850 and did not connect any drives at this point.
As soon as it posted(v slowly, i may add) it allowed me to get into the bios and after a few seconds rebooted (CPU temp was at 29c) so i reseated the ram (ram is in correct slots) and then retested. Same problem.
At this point i set the BIOS to default failsafe values and it still rebooted randomly while in bios-
I then retested with different memory and GFX card and power supply.
I then RMAd the board thinking it was bad. THe new board is exactly the same and im completly dumbstruck. This system does not have any drives connected to it. I then reseated the CPU and changed to a spare heatsink arctic 7 pro and it still rebooted. i tried getting into the bios to change the memory timings and they were at 5,5,5,15
Any suggestions would be appreciated!

i checked the psu cables I have a seasonic 500w PSU and a 600 tagan PSU
both generate the appropriate amps on the 12v line. Both PSUs have been tested on my other pc as well.