This can be caused by a broken spring. Easy to see, as shown in the picture above - the spring above the door will be in two pieces. I have replacement springs, this needs to be done by a door technician as the springs are loaded with high tension. Contact me to arrange repair.
This may be caused by a broken hinge. Cracked or broken hinges can be picked up on a regular service. It is recommended that you service your door every 12 months.
Cables can come loose from the drum due to lack of spring tension. The springs can be adjusted as they lose tension over time.