I'm not sure what the bass were doing; but you did say that you saw a nice big one and that you threw everything in the boat at it and it would still not bite. My guess is that once you saw the big bass you got really excited and you probably sped up your retrieve, in return it was to fast for them and they would not bite it. If I were you I would just act like a fish wasn't there and fish it slow as fishing 30 ft. of water in the dead of Winter. Of course some guys won't agree with this but this is what I would do.
8-)