I'm fairly new to linux so I can't troubleshoot it to save my life but I had a similar problem, I couldn't do anything with my 2nd and 3rd cards. I tried and tried to find a solution but finally gave up, reinstalled ubuntu and followed the guide from the second post of this thread. I don't know what my problem was but I haven't experienced it since.

3x5830 each hashing at 297 Mhash with no overclock.