Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
That probably indicates that the cooling fan is not working, and/or that the cooling passages and the cooling heatsink have excessive dust on them and aren't acting as cooling very well.
(Seriously, a very small furring of dust on a heat-sink can make it remarkably ineffective. Cleaning out all dust thoroughly, from the cooling passages interior to the projector, is probably the second thing to do... after making quite sure that the cooling fan *is* running and running quite fast enough.)
An overheat condition of the lamp will be sensed by the projector, and it will shut down the lamp, in order to prevent the rather pricey lamp bulb from blowing out.
Let me know what you find out... there can be different things wrong than what I just said, and if what I have recommended does not help, I will advise you further.
(And if this answers the question fully, please rate my answer - a five-star rating would be appreciated in that case! Thanks.)