No video from Mini DisplayPort with XFX Radeon 6870 HD

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Feb 13, 2012
p8z68-v pro
amd radeon hd6870
Classic Mac
Mobile Phone
First the setup:

Board: P8Z68-V Pro (Haven't updated to the 1101 bios yet)
Processor: i7-2600k
Graphics: XFX Radeon 6870 HD (2x DVI, 1x HDMI, 2x Mini DisplayPort).
OS: Lion 10.7.4

At the moment I'm running flawlessly with 2 screens (2 LG's) with one hooked up to DVI and the other to HDMI.
Yesterday I've finally bought the 27" Thunderbolt Cinema Display. I figured I should have no problem considering I have
mini displayports on the card and people are reporting they're working out of the box. I'm getting, however, no video.
The screen doesn't turn on at all.

Setting graphicsenabler=no doesn't help.
Tried unhooking the other screens, and various combinations like (only DP+HDMI or DP+DVI) but nothing seems to work.

Haven't tried hooking up the display to the HDMI/DVI ports yet because I don't have the adapter but if all else fails I'll go this route.

What things could I check before I'm forced to try plugging it into HDMI? (i'm really bent on getting this to work on the display port because it means I can run it at the native 2550x1440 res instead of compromising on regular HD res. It's just not worth the money if I can't run it in native res.)
Can't help you on the Mini Display port issue, just wanted to mention the 6870 DVI supports 2560x1600 as well as Mini DP so if you do have to go down the route of an adaptor you should not have to sacrifice the resolution.
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