Infocus 250 projector won't power up

Question

This projector was working fine but when unplugged for any length of time it won't come back on. If you unplug and move to another room in the school and quickly plug in it will come on. We used it in the school library and someone unplugged it and it sat overnight now it will not turn back on. Do you think it is the bulb, ballast, or what? We need it at school and I am trying to figure out what the problem is. Thanks