Install GPU-Z and see how many cards are there. It should be 4 x 7900 series. If not then there is a problem in your sistem...
all four are there however the OpenCL check box is unchecked and it will not allow me to check it. so confused!
Then you have to reinstall the drivers.
uninstalled and run amd's clean uninstall tool. then reinstalled the drivers. still no dice.
What version of the Drivers are you using?
I have tried;
radeon-crimson-16.7.3-win10-64bit
non-whql-win10-64bit-radeon-software-crimson-16.9.1-sep7
13-12_win7_win8_64_dd_ccc_whql-[Guru3D.com]
Trying to see if its something to do with opencl but not sure how to uninstall it or if that is even an option
EDIT
OK so i fixed it, I usually access the miner by remote desktop but instead i turned it off and plugged a spare monitor into the card that didn't work. turned it on and instead of taking the usual 10 seconds to fire up it took like 2 mins but when it finally loaded the desktop i can now see all 4 cards in gpuz. Not sure how plugging the monitor into the second card made it spring to lift but i'll chalk it up as a win.
thanks for replying to my questions
JWGeek