My murry lawnmower won't move when put in gear. The stack pulley turns, the belt turns when in gear but the drive pulley doesn't turn. Does anyone know what the problem could be? Also , I can push mower when it's in neutral

When its in gear is the belt under a good tension or can you easily deflect it?

Have you recently had one of the rear wheels off of the mower?

Belt seems tight, and I haven't had a tire off. I was mowing the grass when it quit moving

Is it hydrostatic or 5-6 speed?

5 speed. Not sure about hydrostatic

I just re read your post and Ballenger is right. If the pulley on the transaxle is not turning then there is a problem with the tension on the belt. There should be a pulley with a spring attached that is supposed to keep that belt tight when your foot is not on the pedal.

The belt is tight, it spins when in gear but the drive pulley won't turn, I can't make it turn even manually

If you can push the mower and both wheels spin freely but the pulley on top of the transaxle will not turn then you need a transaxle. Most repair shops will not repair transaxles.

Thanks for your help, that's exactly what I didn't want to hear!

The good thing is that transaxle was very popular in Murray and Craftsman mowers. You should be able to find a good used one fairly cheap.