I have a craftsman lt1000 mower that has new battery, full of gas, new blades, new gear shift, new axle brackets and cranks great. However, while I can engage the blades with no trouble, I cannot get the mover to move forward or backward. After brief review of the belts, it appears the drive belt seems loose but is not damaged or coming off. The mover won't move. By the way... already checked the tire keys... all is good there. It seems the drive won't engage to the gear I select.

Make sure the blade is off or removed before doing further testing. When you release the clutch/brake have another person observe if the drive belt is actually turning the large pulley on top of the transaxle. If the pullet turns but you aren't moving check that pulley too, it too is keyed like the wheels on the axle