Third display not showing desktop

[DriveJunky95]

Scenario:

I'm running Windows 7 with all updated drivers. Three monitors are connected to a Radeon HD 6870 video card (2x DVI, 2x DP). The two working monitors are connected via a DVI-HDMI adapter and DVI, the third and not-working monitor is connected via a DP-DVI active adapter. The adapter, the screens and the video card are all brand new. My main screen default res is 1920x1200 and the two side screens are 1920x1080. Both vcard and chipset support eyefinity.

(Working) Acer 23" 1920x1080 connected via DVI (top DVI slot on card)

(Working) Samsung 25.5" 1920x1200 connected via DVI to HDMI adapter (bottom DVI slot on card)

(No signal, black screen) Acer 23" 1920x1080 connected via active Displayport to DVI (left DP slot on card)


Problem:

While Windows 7 recognizes the third monitor (has name, native res, and extends the desktop correctly), the monitor is saying that there is no signal and the screen is black (**but my mouse will disappear off the edge of my screen**). I'm gonna play around with cords, resolutions, switching around inputs on the card, etc but for the time being does anyone have any idea why this might be happening?

Please don't tell me I need another active adapter.......

EDIT:

-The third monitor does work, I tested it.
-Tried a DVI-VGA adapter(Samsung), DVI(Acer), and DP-DVI active adapter(Acer) combo. Windows loaded to the log in screen and after log in all 3 screens were black (weird)
-Tried a DVI(Samsung), DVI(Acer) and DP-DVI active adapter(Acer) combo. Same results as above.

I find it very hard to believe that the combinations of cord types so far have all been incompatible with a 3 monitor setup....

The video cards' DVI outputs are DVI-I and DVI-D, but I don't think it matters because the oldest monitor (25.5" one) is 2-3 years old. I'm going to try the DP-DVI active adapter plugged into my Samsung and then play with the DVI-HDMI adapter, VGA, DVI arrangements to the Acer monitors.

Do I need to be using some sort of program to run 3 monitors? Is it part of the eyefinity setup? Or I should probably ask this -- Is it not possible to have 3 (or 2 depending how you see it) monitors with extended desktops?

EDIT: I tried using AMD VISION Engine Control Center to setup eyefinity. The program detected all 3 displays and included all 3 in the final group BUT third display is still a black screen...

I KNOW the screen works -- I tested it in a 2 monitor setup. I KNOW the desktop is there -- my mouse will disappear onto the black screen. So what gives??

EDIT: It's looking like only certain DP-DVI active adapters support eyefinity. The fact that Newegg includes it in their item descriptions and AMD has a list of compatible adapters (AMD Eyefinity Validated Dongles) leads me to believe that this is the answer to my problem.

This is the dongle I bought: Newegg.com - KINGWIN DP-3 DisplayPort to DVI-D Adapter/Active Can anyone confirm?