SLI GTX 970 Issue

[Dman621]

I have 2 GTX 970s in SLI and only one will work at a time, this is a new problem they had both been working fine. I recently added 1 Kraken x40 + G10 and 1 Kraken x31 + G10

It was working fine for about 5 minutes then my pc crashed and did an error check. On startup 1 pump repeatedly failed and when I finally got it up and running the second card would only work if it was the only plugged in.

I'm wondering if anyone knows if this is a PSU issue? I don't know if its because mine isn't big enough.

Specs
OS Windows 10

CPU 4.2GHz 8350

MOBO Gigabyte 990fx

VGA 2x MSI GTX 970 OC

Cooling 
1x Kraken 41x

1x Kraken 40x + G10

1x Kraken 31x + G10

PSU NZXT 750w

 

Any help is much appreciated