I have been having this issue for quite awhile now, and have re-installed it many times now. I am streaming to my flat screen to watch hbogo, and I have all the wire pulled and all hardware is working. When booting both monitors will show up mirrored until the ubuntu login screen. The flatscreen then immediately goes to "no signal". I have gone through the process of installing amd beta driver 12.11 without any positive results. My xorg.conf file seems fine after installing, but I also can no longer use fglrx-updates anymore as they oversize my screen and the unity docks disappear.

My card is an ATI Radeon HD5500.

Any help would be great, or if I need to post more info just let me know.