I just built a new computer with an Asus HD 7770 DC 1GD5 V2 graphics card. I have two Samsung SyncMaster 910Ts and Samsung Syncmaster 913v. Windows 8 recognizes all three monitors but will only let me extend the desktop to two. When I try to extend the desktop to the 913v I get an error message saying "Unable to save display settings."
One 910T is conneted through the DVI, one is connected through Display Port and the 913v is connected through the D-Sub to DVI adapter. If I unplug the Display Port the 913v will light up and the desktop is extended across to it. I also updated to the latest driver.