Hi guys, 
 
Ive recently upgrading my rig to 2 cooling loops, as Ive received natman_doo's custom built blocks.
 
Basically ive hooked everything back up, and turn on the rig, and restored the liquid flow through the rig.
 
When Ive turned on the rig a few hours later, nothing happened, no power going to the mobo, or gpu's.
 
On the mobo the 'On Button' itself, along with an LED for Bios profile indicator are flashing like every 2 - 3 seconds, and ive noticed that a white light is also flashing in sync the two lights/buttons above. The white it indicating to me that the 5V Reg line from the psu is the problem.
 
When I unplug the mobo power cable from psu (evga 1300w g2) the lights on my mobo turn off. When I plug in the smaller mobo power cable into the psu, the lights come back on.
 
Am I right in thinking that I should RMA my psu with evga?

Ive taken my 750w psu out of my old rig, and used that to check if my rig booted up, which it did.
I've got an RMA with EVGA now, so hopefully they can check the psu for me.
 
I did notice when i plugged in my old psu, that the 5VSB light is on 

kool will mate, will be posting my rma to evga eu tomo

Glad you found the root of the problem.  Hope you get that cable replaced, assuming its a modular PSU.