windows 8 - Can't enable third monitor after upgrading from Win8 to 8.1

I recently updated to Win 8.1 - now only 2 of my 3 monitors are working, after they were all working perfectly fine under Win 8.

I have 3 x HP E231's running on an AMD R9 280x - One of the monitors is DVI, the other two are Mini-Display Port to DVI.

In Screen Resolution or the Catalyst Control Center, every time I try to enable the third monitor it tells me I have to disable another one.. I can't find much info on the net about this problem - have checked here Windows 8.1 triple monitors - can't enable all 3 at the same time but the guy just brought an adapter - I know all three monitors were working under Win8 so why not 8.1?

Cheers