Mechnical Key Not Unlocking Door

I have a Gen II/2008 Prius and am having issues unlocking the doors. It seems as though the 12volt auxillary battery is dead. I tried jumping the car, but it is so cold now, it did not want to start. Since the car was at a school and I had to get back to work, I locked the door from the inside (FOB was not working) and closed the door. I figured I could use the mechanical key on the FOB to open the door later. This evening, I tried to use the key. It turns counter-clockwise, but not clockwise. I did try to use some pliers and was able to turn it clockwise, but it still did not unlock the door. Any idea what the next step is?