They do not last for ever, any where from 2,000 to 8,000 hours depending tv brand & model #.
About how many hours are on yours?
& what is the lamps rated life? Sometimes they do not last the rated life for a few reasons, sometimes they last more, I have around 10,000-12,000 hours on a 8,000 hours rated lamp.
The lamp is in a sealed (should be, my Sony SXRD lamp is) compartment. Pull the lamp is check for dust, do NOT use any water, window clear or anything like that on the bulb!!! Use a dry very soft cloth & use your vacuum cleaner, DO NOT TOUCH the bulb with your bear hands, the oils on your hands can do damage. Also check the lamp for color distortion, it will either be a black ring/spot or look like a rainbow that is a bad/old bulb.
I am 99% sure you just need a new lamp.