I have a JBL PB-10 Subwoofer, it works fine when the light turns green after plugging the power supply a few times in and out. I dont want to have to do this every time I want to listen to music to my system. The manual says the red light is supposed to turn green by itself so it indicates that a signal is coming into the sub. Is there any way to fix this? Am I using the right kind of cable? I am using a standard red/white RCA cable (I only use 1 for LFE). Do I need to use a subwoofer cable?

What are you trying to use on the other end of the cable? Your computer? A receiver? If so what type is it?
This may help you if you lost the manual:
Owner's Manual

I have a JBL sub...

the light comes on when bass comes on. Don't worry about it. watching a movie with it for instance, it will be off for long sections of dialog then suddenly it comes on with a loud boom when there is for instance an explosion. This is normal behaviour.

I am using a Sherwood RD-6108 Reciever. I just played a really bassy part and there is still no sound coming out of the sub, I have to turn it off, then turn it back on for it to start making bass.