Dell 4610x projectors shutting off

Hey guys,

My school district has about 5 Dell 4610x projectors at one school that keep flickering the projected image and shutting off.  One classroom won't go more than 5 minutes and shuts off. The bulbs have about 2/5 of their life left but they keep flickering the image and then shutting off. The projectors don't give any temp light or bulb light, they just shut down. Any ideas? I've tried changing blubs and blowing out projectors? The heaters aren't on in the classrooms and in some cases the AC is running at 70. We've re-directed the vents so the heater doesn't blow on the projector directly.