What goes up, stops, goes down, stops, and never quite opens or closes all the way? Your garage door opener, of course. When your garage door behaves this way, you need to find out why before you can fix it. Take a closer look at the opener and its components to see if you spot the following.
Birds are absolutely cuckoo. They will build their nests in any place they can, and what better place than in a garage and out of the weather? Unfortunately for humans, this sometimes means that you will find their nests attached to the chains of your garage door opener.
This happens when you leave the garage door open for about a day or two and an opportunistic bird comes along and decides to build a nest right on top of the chains of your garage door opener. When you try to open or close the garage door, the chains stop when the nest hits the front of the opener. The opener compensates by trying to move the opposite direction, but the nest stops the chains at the top of the support bar opposite the opener.
This results in that up/down motion without closing or opening all the way. If the parent birds are not present, you can climb up there to see if the eggs have hatched and/or if the baby birds are gone. Then you can remove the nest and the opener should work just fine.
If your neighbor's garage door opener operates on the same opener frequency, and he/she is trying to open his/her door about the same time, the garage doors get confused. These mixed signals cause the doors to act oddly, but eventually the doors should open or close all the way. It is unusual for them to get stuck halfway because of mixed signals, but not unheard of. Your garage door opener repair technician should be able to fix this problem easily.
Another possibility is that the last time you were able to fully open or close the garage door, you got something jammed up inside the opener. When you went to open or close the garage door again, this object jammed inside the chain motor, preventing the door from opening/closing. To get this object out, the whole of the opener has to be removed, opened up, cleared and cleaned out, reassembled, and then reinstalled. That is a job best left for the repair technician.