well if the car is running and just the belts arent moving then obviously it is something with the pulley... but i dont really know how your car is running with the alternator belt not pulling.

umm... def. tighten your belts... they shouldnt have much play in them at all... maybe 1/4in. at most i would say... i dont really know what else to tell you after that... there is a nut in the middle of the main pulley that may be loose??? idk, check it out maybe