Lisa: Enlighten Me. (Get it?)

Quick question. Does anyone out there know stuff about lamp posts that automatically light up at night? We have a lamp post in our front yard that used to light up every night when it got dark. It stopped lighting up, so I replaced the light bulb, and now it doesn't light up at night any more. It never lights up. Any ideas? There is no switch for the post inside the house. There is a breaker just for the lamp post, but I have made sure it is in the correct position. I can't find any kind of sensor on the post itself that could be obstructed, but even if the sensor WAS obstructed, wouldn't that mean the lamp would think it was dark out and would just stay lit all the time?

Update:
Putting in a bulb with a smaller wattage made no difference. Here are some pictures of the lamp post to help with the detective work. There is a little thing on the front of the lamp post that I thought might be some kind of daylight sensor. It is a little round circle right below the lantern part. It looks almost like a mini bike reflector, with little horizontal lines inside the plastic--doesn't seem to be especially reflective, though.

Here's the lamp post:

Here's a closeup on the possible sensor thingie:

(Click on the thumbnails for bigger pictures.)