Are you pushing the bar in or pulling on it and the mower will either not move at all or will move very slowly?
This problem happens when the drive belt breaks, it is worn out or the transmission has broken or the wheels or their drive gears are worn out or broke. Each of these can be systematically troubleshot to determine what the problem may be.
One of the first things to try is to start the mower and raise the drive wheels off the ground and engage the drive handle. If the wheels turn, you know that the drive system is working but not well enough to pull the lawn mower. This is normally a worn out belt or the belt has come off of the pulley.
If the wheels do not move, then the transmission could be bad, the drive wheel gear slots could be worn out or the drive gears could be broken. This will require pulling the wheels off to inspect the gears on both the wheels and gears.
If they appear to be fine, then it will be time to call a Self Propelled lawn mower repair professional. Visit our locations page for an office near you.