My belt won't turn

I have a 1993 Ford Tempo. My car starts without a problem but the belt won't turn. I have checked all the pulleys and they turn freely. When I start it, it makes a horrible rattling noise. I have changed the belt and the tension is good. I have checked everything. I took the belt off and started it for a second and the noise disappears. Is there anyone who can help me figure out what is wrong with my car before I start sinking a lot of money into it. It has 125,000 miles on it and I don't want to spend a lot of money if it is not going to be worth it. Please help.

Sounds like the crankshaft pulley is bad

Sounds like the crankshaft pulley is bad
Hey thanks, I had that checked and sure enough it had come apart.