So I had to RMA my 750 P2 because after not even a year of use, it started hard rebooting my computer. I just received the replacement PSU and it is exhibiting behaviour even worse than the one I RMA'd.

I'm fairly certain (although not 100%) it isn't any other part in my computer because while waiting for my 750 P2 RMA, I have been using an EVGA 750 G3, and I was having zero problems at all. But literally the moment after I replace the G3 with the P2, the hard reboots start happening again... exactly same issue as the 750 P2 I sent back!

I'm at a loss of what to do now. Why would the 750 G3 work fine and the P2 doesn't?

Can someone shed some light on this? I really don't want to have to wait for another RMA and then experience this problem for a 3rd time. Is this a common problem with the P2?

Great question there Saj!! Id also start looking at where you have this pc plugged into the wall. You may have a AC unit or other things farther down the line on the same breaker run that are creating a lot of noise and voltage drops that are messing up your PSU's.

I used the G3 with my P2 cables. I heard mixing cables isn't a good idea, but... the G3 worked perfectly for the 10 days or so until I replaced it with the new P2 today. Then the hard reboots started again, just like before.
 
Is it possible that the P2 cables are somehow damaged to the point they won't work with a P2 but with a G3? Seems a bit far-fetched.

Just to show you what was happening before. This was the P2 PSU I sent back for an RMA:

youtube.com/watch?v=DLUlhlYt_BM

And this is the new P2 I received:

youtube.com/watch?v=hOt3sVIowvk

But none of that ever happened with the G3 using the exact same cables.

As you can see I've gotten a new case, new CPU heatsink (thought maybe it was heat issue). I've been replacing parts trying to fix this issue and so far the only thing that seemed to work was swapping it out for G3.

In general it's always a good idea to replace the cables when you put in a new PSU just to be safe but in this case I agree with Sajin and would recommend an RMA.

Ohhhh myyyyyyy goddddd... OK so I just swapped out the video card PSU cables for a couple back-ups from my P2 box... the hard reboots have stopped. I'm running Furmark with no problems.
 
I guess the cables are defective.
 

Sajin

 
Hope the issue is over now. I don't see how you got away with running defective cables for 10 days on the G3. Did you not stress test the system in those 10 days?

Yeah I did and it worked fine. I'm guessing the cables may work fine when they're oriented in a certain manner, and perhaps they were in that orientation with the G3 but with the P2 no dice?

In my old case, they VGA cables were pretty crammed in so perhaps the bending over time degraded them in certain positions? I guess I'd have to slice them open to take a look.

congrats getting it running

Probably just a bad unit. Time to get another replacement.

Your call at this point. If it were my rig I would try another psu. 

The 750 P3 worked fine, but both P2's act up?..Wow, weird.
 
Flip the ECO Mode switch and see if it matters..There were problems reported with ECO Mode on some units a while back.
 
Disconnect everything from the P2 and use the 24-pin PSU Tester as described in the manual to turn on the unit and see if it runs, and stays running for a little while.