I just picked up a pair of 960ftw 's, and was hoping to install and run them for a wile until i build a new system.  So i had some evga 285 ssc in sli running fine on a x58 sli mombo. after installing the card the computer go's in to an infant boot loop. as soon as the windows 10 x64 logo comes up is restarts sometimes instantly and some time after 5-10 sec's. I was running a corsair mx 1000W PSU. I just tried a evga 1300W G2 PSU and have the same problem. I have the latest bios but thats from that last one put out in 2011. I switch the cards in the two 16x pci 2.0 slots, made no difference.  If i only install one card I have about a 75% success rate of booting in to windows and the computer running normally. I reset the bios. undid the over clock and put back to stock, removed the battery and waited. My temps are fine.
 
Evga x58 sli mombo
Intel i7 965 extreme
corsair dominator DDR3 1600MHz 12GB
Evga gtx 960 FTW x2
Evga supernova 1300W g2
LG BD-RW
dvd RW
on board sound
Samsung 850 evo X3
Koolance cooling
 

it will start and run first boot 75% of the time with ether 960 one installed. just not both.
DDU? I was able to boot with one card and remove all the old drivers and install the new ones but it didnt make any difference.
 

Sounds like a motherboard issue.

Just saw your post today. Glad to hear that everything is working now!