It may be the green handlebar clamps are slightly out of position. Open the clamps and pull up the handlebar as much as you can and then reinsert the clamps. Try starting the mower after you do that. If it starts, pull it backward to see if it continues to run. Then push it forward to see if it continues to run or stops. If it stops when going forward it's the clamps. Also, did you hit something in the yard and did the mower or battery indicate any color other than green when it stopped?