Guys / Gals

I need some advice.
All of a sudden my most stable rig is no longer stable.
One of my GPU's (RX 480)keeps dropping to 0.00 Mh/s sometimes it wont even start hashing when I start the mining software.
It was perfectly fine yesterday.
I have tried to re-install the driver to see if this was the cause.
I even selected -di 4 and ran it on its own.....when running on its own it runs perfect. But as soon as I try to run a full rig the card fails.

My PSU is a EVGA G2 1600W so that is more than enough power to run 7 cards.

I have the exact same set up on another rig and that runs fine.