The most common roller garage door problems are: the door won't close or open, or the door falls instead of normally sliding down (the most dangerous problem). If the garage door won't close or open, the problem may be the door opener, which may need to be reprogrammed to start functioning again. When the door falls instead of sliding, the door's extension springs are often to blame. Worn out and damaged springs generally require you to turn to professional repair services due to the dangers of such a repair.
External Sources:
Quick and Easy Garage Door Fixes
Roller Garage Door Resource