Today I tried to install Ubuntu 12.10 to my machine, but all the time I encountered the same problem, I successfully boot from Ubuntu 12.04 DVD, and a purple background comes up with accessibility and keyboard icons at the bottom of the screen, then when you wait a while a monitor text comes up "No signal" (Keep in mind that this signal is only shown when there's cable in the monitor HDMI plug), and nothing happens, a little later disk drive stops flashing meaning that disk finished being read.
Even if you reset the computer you still get no signal, you have to turn the power of and on again, and plug HDMI out and put it in again.
Graphics card: ATI/AMD Radeon HD 4850
Connection to monitor: HDMI
Monitor: Samsung SyncMaster T220HD