Ohhh, interesting!
The Corsair TX750M is a good unit. It's manufactured by CWT (a decent PSU OEM), I believe . I'm running a TX850v1 and a TX850M myself at the moment. That said, it may still be that you're overtaxing the poor thing.

/sign :-( that's possible.
I'm using a XFX 1000W Pro Series 80PLUS Platinum. With a little OC and voltage@1,12v 3 cards are pulling ~750w (power meter) out of the wall while scrypt mining.
This system based on a Sempron 145, 8GB RAM, 2 fans and a SSD.
Larger oc@1,2v = ~810w
I get similar problems if I don't give them enough core voltage. Had one 7950 with bad ASIC quality, it got SICK/DEAD really quick.
Good luck!