And God said "Let there be light" and there was

NOT!!!! Well not on my deck anyway! Okay - short story. This started on the Tuesday before Thanksgiving. My motion light on the deck had gone out. Well, actually it stayed on all the time and then finally just went out Dave came to look at it. New lights, says he. Off to the store I go for new lights. Ahhh not the problem. So off to the store I go to get another unit. This time instead of a motion detector I chose a dusk to dawn one. Dave comes up, hooks it up...no light. Junior comes over and fools with it..no light. Finally I tell Dave just screw into the wall so I don't look like trailer trash with my light hanging off. Which he does. Well low and behold doesn't the darn thing come on that night all by itself! Just like it should. At dawn off it goes. Great don't know what the heck the problem is, who cares?it's working. Thanksgiving night works again. Just like it should. Comes on at dusk and off at dawn. And there folks ends my story. The light is no longer coming on. Two nights..it worked for two nights. I'm beginning to think something is afoot err alight. Anyway, I am looking for helpful suggestions. I like having my deck light. It gives me a sense of security - I know - I can hear ya'll now....You never even lock your doors and yet not having a deck light throws you into a panic! The answer to that would be a resounding YES!! Don't even try to figure it out. Greater minds than yours have tried and failed. We each have our own little quirks - okay so I have way more than most - but not having a deck light is definitely at the top of the list - at least for this moment it is. HELP!