2nd and 3rd monitor not working on Radeon HD 7900 Display Ports

I Radeon HD 7900  with 3 NEC Monitors, all used DVI-D.


The main monitor is connected to DVI and works find, the other 2 are hooked up to the two Mini-display ports via an DisplayPort 1.2a to DVI Active Adapter BUT my computer is not even recognizing the monitors.


Please help.