This is a common problem with certain Toshiba DLP's. My brother is having the same problem.
There was talk of a redesigned bulb at one point that might get you a little more life out of it. My brother is thinking of ditching his for an LCD.
Search google, there is plenty of threads about it:
http://www.audioholics.com/news/edit...-lamp-problems
I have a Samsung 71 inch DLP and I am still on my original bulb after a few years.