lawn mower will not move

This will get you started. You check the drive belts and pulleys

https://www.ehow.com/how_6511711_troubleshoot-murray-mower-won_t-move.html

Also the gear linkage must be checked to make sure it engages properly and you have no sheared key on the drive shaft. They have several manuals here for your model

https://www.murray.com/na/en_us/support/manuals/results.productmanuals.html?searchrequested=309304