I think it is power issue. You said you tried a second psu but of the same power? Try a better psu and see if It changes anything. You cant rule out power just because you tried an replacement that is exactly the same as the original. Your best best is the process of elimination and It's best not to leave anything out or you will find yourself backtracking and wasting time.
could also possibly be the cpu.
could also possibly be the cpu.