I think my problem has already been solved in other posts, but I have not found
I'm on a 64bit debian wheezy, and I have two cards Sapphire 6870, but could not make them work properly.
fglrxinfo Error: unable to open display (null)
I tried with drivers free + nonfree firmware with proprietary drivers (versions 12.6, 12.8 and 13.1), but I still have this problem.
I have no error during the installation, I can not find the source of the problem.
If a person who has had this problem and found a solution.