I have I computer that have no monitor attached. When I boot it X fails to start because there is no monitor detected. If I boot it with a monitor attached and after X is started I remove the monitor everything works fine.
Details and Background:
This computer is a kind of hardware consolidation server. It's only purpose is to run two Virtual Box VM's that run Windows XP and some important but seldom used (once or twice a month) programs. For a couple of time it has been lying in a corner with an old monitor attached to it and working great.
But space in the office was getting scarce and I moved the computer to the server room. There is no monitor attached to it there (no space), and sometimes the computer is rebooted. When it boots without monitor X is not started, the vms don't start and I get called to solve the problem.