There are a few reasons why a garage door will not close. The first is that your photo eyes at the bottom on each side of the garage door are out of alignment or something is blocking their reception. These sensors are there as a safety device so that nothing is crushed under the door. This only affects the door closing. Usually the door starts to go down and then reverses or will not try to close at all.
These sensors have a red light on one & a green light on the other, check to be sure that they are lit. One is a sender & one is a receiver. They must be pointing directly at each other to operate correctly. The photo eyes are attached with wing nuts which may be loosened to allow the proper alignment of the eyes to be set and then retighten, again using the wing nuts. If the photo eyes have been aligned correctly, your garage door should close normally.