I need help with the sound system in my car?

I have a 2000 Infiniti I30 with a factory installed 7 speaker Bose audio system, which includes a subwoofer. However, I had just recently realized that my sub is not working at all. I turn up my music but the sub is not even budging. The funny thing is that all this time I thought the sub was working. Anyways, I checked the fuses and the connection and everything seems to be fine. A friend of mine said that whoever owned the car before might've disconnected the sub so as not to hear the thump. Well, I'm hoping that's the situation so I can just connect it again. However, I'm thinking that it might be just broken and then I'll have to get a whole new sub and amp. Either way, I'd rather pay a lot less and have somebody connect it then spend $450 on a whole new system. What is your opinion? Is the sub out or is just disconnected? Any input would help, thanks.