P2 4 pin connector causing shutdown on my pc?

Hi i have been battling with my new (2nd hand) computer all day as after rearranging some psu cables it decided to no longer boot properly, it would start to boot after pulling everything out and testing it after each cable was installed i found out that it was the 4 pin connector running to the cpu with "p2" stamped on it that is causing the outages. all other power cords are fine but what the hell do i do no? could it in fact be the cpu or the cable itself? any help would be very welcome as i have gotten very few hours sleep since this problem arose. thanks alot