dual monitor won't work windows 7

Dear: All

 

dual monitor won't work windows 7 and i have 2 ATi card monitor and 3 monitors just 2 monitors work mirror and on not work and all the driver installed but in the device manager under monitors there 1 Generic PnP Monitor and under Display adapter AND FirePro v4900 and the standard VGA but the FirPro v5900 can't found.

 

Note: My pc HP compaq Z620 Workstation .

 

Best regards