Why are my subwoofers not working?

Question

I took a long trip recently and my subs kept failing at random points. The rest of my speakers were playing fine, but the subs just faded in and out. I took a cursory glance at a rest stop and assumed it was the connection to the battery, which was loose. Today, I tightened it up, but now they're hardly working at all. I can't see anything else wrong with them. I have an embarrassing lack of technical knowledge, so I was wondering if anyone had any advice? Thanks.

Answer 1

just test the subs with batteries.

if they don't make a popping noise then they are broken

Answer 2

first thing, check all your grounds, number one thing wrong, usually solves alot of problems.  

second when the amp wire was loose you may have blown a fuse, check the inline fuse on your power wire along with and fuses on or in the amplifier itself.

third check RCA conections, speaker wires and gain levels

Finally if it still doesnt work, check your amp and subs with a friends system to see if one may be blown.