What is wrong when the motor is working but the treadmill isn't running ?

Possible causes include but are not limited to:

Gear or pulley not secured to shaft (If it uses a grubscrew, that may be loose)

Gear stripped or otherwise damaged or pulley broken

Broken drive belt

Once you have an idea what is wrong, you MAY be able to get more advice and possibly spares here:

http://www.body--sculpture.com/index.php?action=contact
Broken shaft

Just THINK
February 2017