I'm also having the same issue as above with a PowerColor Radeon HD 7950 (v2)
This card has two fans. It has two DVI ports, 1 HDMI, and 2 mini Display ports.
The port at the first level (at the fan level horizontally) does not work. The DVI port at the board level horizontally works.
DVI HDMI mini1 mini2
The DVI port that doesn't work is the one below. This is what I call the first level (leveled with fans horizontally).
The DVI port at the side of the HDMI works.
My monitors are both using VGA with DVI adapters. Each of them works if plugged to the working port. Each doesn't get detected when connected to the other DVI.
This is the card: http://www.powercolor.com/us/products_features.asp?id=418
It says DL-DVI-I/ SL-DVI-D for DVI Output. Maybe it has something to do with this.