I had same problem and it was clean up time and ensuring the bulb made contact [it wasn't ] with the positive plate at base of bulb holder. I found when bulb was replaced it wasn't touching the plate a little adjustment to the plate and it worked I used a new one tested the original that was ok so kept for spare.
Also ensure the bulb sides [if using original] and the holder sides are clean to get good negative contact.
bob, June 2011
