I have 3 monitors, with two ATI 6900. I want to use all monitors using DVI. Is this possible? I'm using Windows 7. I can only get two of the monitors to work at the same time.
Ensure you don't have CrossFireX enabled as when it is enabled then the video ports above 2 will be turned off so that performance of the two cards can be combined and delivered on those primary and secondary ports (only).
Multiple Monitors with ATI CrossFireX™ Configuration
◦ When ATI CrossFireX™ is active other display devices other than the primary and secondary monitor connected to the Digital Video Interface (DVI) or Video Graphics Array (VGA) are rendered inactive.
Other than that, we'll need more exact info, like card models, configuration, ports tried, etc.
It sounds to me that you probably have two ATI Radeon HD 6900 series desktop graphics cards?
If that's the case, you can get all three working using DVI. However, you will need at least one active (not passive!) mini-Displayport to DVI adapters. I have a similar setup, and this is how I got mine working. Hook up all three monitors to the main graphics card (try both--if it doesn't work on one, try the other). Two of them can plug into the two DVI ports. For the third monitor, you will want to plug it into your active mini-Displayport to DVI adapter, and then plug the adapter into one of the mini-Displayport connections behind your graphics card. Then you should be able to use all three monitors while in Crossfire mode.