Please help. I have a Bose 321 Series III system...

Please help. I have a Bose 321 Series III system & there is no sound coming from any of the speakers. The CD player works fine-- so I don't think it's the "media center" part of the system.

While troubleshooting, I did notice that as I unplug the power cord from the subwoofer-- there is perfect sound coming from all the speakers and that the sound coming from the unit is very nice-- the only problem is that it only lasts a fraction of a second & sound only comes from the unit as it's being unplugged.

Please advise-- I love my Bose system & only wish that it worked better for me. I would also like to know which main part is most likely to be defective as I'm willing to buy the powered sub or media center off eBay as this system is no longer under warranty & the store I bought it from (Circuit City) is no longer in business.

Thanks for any advice you can give me...