Remote control won't turn projector ON

I work for a company that has a 2100MP and a 1100MP. The 2100MP is mounted on the ceiling. The remote control will not turn the projector ON, but it turns it off and functions normally otherwise. The remote for the 1100MP controls the 2100MP in every way except for turning it ON as well. Why can't I turn the projector on using the remote anymore? It used to work.