Faulty ax860?

Having problems with stability with my new build.

Intel i7 4790
Gigabyte z97x-ud5h-bk
G skill pc 2400 (off mobo rec list)
Samsung evo 840 500gb
Corsair Ax860
Corsair h105 watercool
Gigabyte gtx 770 4gb x 2

Any load on the system and it shuts off.

I've turned down settings, removed all ram and rotated through the sticks individually. I pulled one then both gtx 770's and just used the built in video (was worse/turned off quicker) and nothing has worked.

Pretty much I have nothing plugged in and any load shuts the computer down. Faulty psu? Is there anything else I can try before going through the hassle of ripping out a psu from another computer and replacing the ax860?

thoughts?

Thanks

Besides the 24-pin ATX power connector, you also connected either a 4 or 8-pin plug from the PSU to the 8-pin ATX12V connector?