This issue is caused by the projector not having the correct input selected. Most projectors have multiple inputs to be able to support different PC's, TV's, Laptops etc. To fix this you can change the input of the projector by pressing either the 'Source' button until you get a picture or if there are specific buttons on the remote for the projector, pressing one of these should resolve the problem.
That didn't fix it
You may want to check the cables at the back of the computer are all correctly plugged in. Make sure all the cables are fully into the back of the computer and then try changing the input of the projector again.
If your problem is still not resolved then contact your I.T department who may be able to help and if not they will contact us to help resolve the issue.