I know that there are many similar threads on similar topics, but I have been pulling my hair out for this particular issue and have decided to ask the community at large for some help.
So I have configured a dual boot system with Windows 7/Windows XP x64. The dual boot configuration works fine.
I have 3 monitors in portrait mode, with two HP LP2476W monitors and an older, cheaper Samsung Syncmaster 226BW.
My graphics card has 2 x mini DP inputs, an HDMI, and 2 DVI inputs. I know that for a 3 monitor setup, at least one monitor has to use the DP input.
So I've got both HP monitors with a DP-mini DP cable and the Samsung with a DVI cable hooked into the card. On Windows 7, everything works without a hitch. I get all 3 monitors up and working just great, so I'm sure it's not some sort of a hardware issue and I know that the video card can "recognize" all 3 monitors.
However, when I boot into XP x64, I can't get all 3 monitors to work. I have downloaded all the latest drivers for the monitors and the video card, but I can't get all 3 monitors to show at the same time. What's more, I can get any 2 out of the 3 monitors active at any given time, showing that it's not a problem with a particular monitor or connection, but I just can't get all 3 active at the same time. If I go into the Computer Management tool, I can see "AMD Radeon HD 6800 Series" under the Display Adapters, but I cannot see anything related to my Samsung monitor (even though I can see all 3 monitors under the Monitors portion of Computer Management.
Am I missing something here? This is driving me crazy!