What kind of connector do you have running from the projector to the computer?
It sounds like it isn't hooked it correctly or the machine doesn't read the projector correctly when it is connected.
You know, I am not sure. I don't think it is an s cable, optical perhaps? LOL. I know nothing about wires I'm afraid. I am acutally trying to help my husband find the answer to this and I can't ask him right now. I know a little about computers but wires and connections....zip.
It was up and running before the man who installed everything left. To my knowledge nothing was changed from what he did. It worked until we shut the computer down and the next time we couldn't get the projector to come on or display anything.