1) ALWAYS look the cable around the stap:
2) Open the bass up and see if all the wires are still solid. If not a little soldering will fix that. If you dont know how, its a VERY useful skill to learn, so learn it.
3) Run a new cable in and see if the old one is broken. I always use Planet Waves cables as they seem pretty much indestructable (the standard one, not the classic one). If the old one is broken, just throw it away and get a decent cable that will last you for years.