Volume doesn't turn up.
 

This morning I started my car and went to put in a new CD. I hit eject, took out the old one, then tried putting the new one in. It said CD Error. I tried again and got it to go in. The CD started playing, so I cranked up the volume. Nothing happened. I can't get the volume to go past a certain level. It is very low (almost low enough that you can't hear it while driving). The only mods I have to my audio system is an aftermarket amp and subwoofer which was installed about 5 months ago. I still have the stock H/K radio unit and radio face.

I took it to the shop that did the subwoofer install, they played around, disconnected the battery, looked at the amp and sub, and came to the conclusion that the problem is my radio itself. They said that maybe if I unplug the battery for 30 minutes that it will reset everything. I'm afraid to do that because last time I did, my ESP unit got fried and the dealer had to replace it. I can't afford to try that again because now the dealer will probably give me warranty issues about my subwoofer, amp, and NOS.

Please, does anybody have any ideas or experience with this type of problem? Thanks!