I am so pissed off. My favorite battery pack that I matched myself has a battery that is getting hot.

I raced last Saturday in the A-Main with this pack, and left it in the car until yesterday. I figured it still had a good enough charge on it to store it that way. I guess I was wrong. I took off the battery and put it on my bulb discharger and the lights didn't light. So then I threw it on my equalizer and none of those lights lit up either. Then I got worried. I threw it on my ICE on 4 step, and after about 2500 mah one battery was getting quite hot. Is there anything I can do to save that one cell? What happened to it, did it reverse? I can remove that one cell, but I am so pissed, that pack was made of my best batteries ever arghhh!!!