will not move when clutch is dpressed?

If this machine is a hydrostatic drive it may be in by pass ( push mode ) depends on what make of machine it is as to where the by pass lever is, most ride ons have a simple idler pulley to tention the belt which creates the clutch

Husqvarna man
June 2010

this is for a Suffolk mower
not enough revs on the engine
speed the engine up till the cutting blades start to rotate via clutch centrifugal force, now engage the clutch by pulling the lever close to the handle, the mover should now drive forward release the lever to stop the drive motion,no drive movement belt is incorrectly adjusted , with the cutting blades spinning you can cut in tight corners just by pushing mower back and forth

wirecutterman
June 2010