Audio Systems: surround speaker problem, weird mode, faint hum

Question
I am having trouble getting sound form anything but the center speaker on my surround system. I can hear a faint hum in both the front and rear speakers, but only actual sound comes from the center speaker. I have tried the test mode on my receiver and all I get is sound from the center speaker. Any ideas?  

Answer
I'd trouble shoot it by disconnecting the center speaker and hooking it up to the other channels one at a time.  this narrows down the problem of wether its the speaker or the reciever since we know the center speaker works.
you can also try the opposite of connecting the other speakers, one at a time, to the center channel of the reciever to test each of them, since we know the center channel of the reciever works.
my guess is that either channels have blown in the reciever or it's in some weird mode that needs to be set right.
what kindof reciever is it? (actual model number please)
thanks, and good luck!