Insufficient Power = 2nd GPU Not Recognized?


Dec 16, 2017
I just updated my processor and its drawing enough power more than the old one to put me near the max of my PSU (650W). 2x 7950s were working before the upgrade, now only one is recognized (BIOS, Radeon options, CPU-Z, Device Manager). But the fan is running on the unrecognized GPU. The boost button light turns on the 2nd inactive GPU as well.

I used power calculators beforehand and it put me around 630-640W under load w/o overclocked, which I've disabled. I've swapped the 2 cards into the primary slot that is working, and they are both functioning fine on their own.

Would insufficient power cause the 2nd GPU to not register? Does it deactivate itself to save the computer? Why are the fans running fine then? What else could it be? Before I run out and buy a new monster PSU or external one, I wanted to make sure this is the issue.

Thanks for your help!
Yes absolutely, if a card doesn't get the power it needs it will turn off and not be recognized. especially with multi rail PSU's. What PSU is it?