I have a similar problem with my Samsung 22" LCD.
Whenever I start my computer I MUST turn the power off from the monitor and then turn my computer on. Give it a min or so until my G15 keyboard lights up and then turn my monitor on.
I turn my computer on while my LCD is already turned on it will stay in standby until I shut down the computer and do what I described above. I have no idea why it does this but maybe you have a similar problem.