Garage door cables are the strands of wire bundle together to form the cable that assist in lifting the garage door. These cables are typically constructed of aircraft aluminum or stainless steel. The cables attach on both sides of the garage door to the bottom brackets on the garage door. The cables then run up the height of the garage door and wrap around the drums. The drums are attached to torsion tube. The torsion tube also holds the springs that are wound to provide the counter balance or force to open and close the garage door. This is in a torsion spring system. In an extension spring system, the cables attach to the bottom brackets on both side of the bottom of the garage door. In this system the cables run up the height of the garage door and then through a system of pulleys attach to the springs on both sides of the garage door. In this system the cables still do the lifting while the springs still provide the counter balance or force to open and close the garage door.
If your cable are loose this could lead to a more significant problem, and great caution must be used as either type system is under a great deal of tension.
*Note: Working on the cables without the proper training and tools can lead to serious damage and injury including death.
If your garage door cables are loose it could be as simple as securing the torsion tube and torsion springs and then rewinding the cables. This simple for a garage door technician but is very dangerous if you do not have the proper tools and training.
Loose cables could be a sign of something more serious:
You could have broken or failing spring or springs.
Your door could be out of balance.
Your door could be off track.
You may also have rollers that have failed or fallen out of the track.
These are just examples and these or other factors not mentioned could have caused the cables to come loose or loosen.
The loose cables are the symptom of some other problem. I would recommend having a Veteran Garage Door Technician inspect the garage door system and make recommendations based on that inspection.
*Note: Garage doors and garage door springs and cable systems are dangerous and can cause serious damage and injury including death. It is recommended that trained garage door technicians perform these inspections and repairs.