The "overhead projector" has long since been retired in favor of the document camera/video projector combo.
It is easy to use and even if you are not sure how to operate it, more than one kid in the classroom should be able to help sort it out. The most common problem is selecting the DocCam as the source for the projector.
Three years since they started arriving in the classroom, even I can usually sort out any connectivity problems and get it working. It is usually the first thing I do after reviewing the lesson plan to see if I'm going to need it for the days lesson.
So, here I am in a 2nd grade classroom on the first Monday after the Thanksgiving week with only 20mins before class and I'm in totally stumped trying to get the stupid thing to work.
The projector is on, the doc/cam is on, the cables are connected and nothing is working. The video projector is "searching", without success, for an active display source. The old standby reset solution of power off/on did not help. The tech-savvy teacher next door couldn't get it to work either.
We made do with the old-fashioned whiteboard and dry-erase markers for math lesson.
It wasn't until after lunch that the school custodian suggested an answer -- mice!
It seems that mice have recently developed a taste for plastic cable sheathing and are gnawing on some of the computer cables in the ceiling and under the classroom floors.
One teacher even reported, with some irony, that she came in one morning to find her computer mouse cable chewed on, presumably, by one of its real world cousins.