1998 Chevy Lumina serpentine belt not turning

I replaced the alternator about 6 months ago and everything ran fine. But I have not driven the car since then.I cranked today, the car it started fine but I started to notice a small amount of smoke coming from the engine. As I looked closer I noticed that the serpentine belt was not turning at all. As time went on, the car was still running, the smoke started to get worse so I shut off the engine. Back when I replaced the alternator I noticed one pulley at the bottom of the serpentine was spinning almost freeley and making a funney noise but I don't know what that pulley is. Any ideas what might be the problem? Thanks for the help.