1995 Toyota Corolla Water Pump Won't Move

Engine Cooling problem
1995 Toyota Corolla 4 cyl Front Wheel Drive Automatic 174K miles

Hi,
I've got a bit of a strange dilemma. While I was driving down the road the other day, my engine started screeching loudly. I took a look under the hood and found that the belts were barely moving. It looked like one of the pulleys was refusing to move, and the rest were trying to. Since the car was still able to run, I drove it the rest of the way home anyway. After a few minutes the screeching stopped, and my car started overheating on the way home. When I got home, I realized that the water pump was leaking badly.

I then bought a new water pump and replaced the old one. I started the car and heard the same screeching sound. I loosened the belts and found that the water pump pulley was again refusing to move, even though I had just replaced it. Any ideas?

Thanks,
Chris