If one blade has suddenly stopped turning, the pulley will stop turning and it will burn up or shred a belt. You might hear a squealing sounds or smell some burning rubber but not always.
A few things can cause the lawn mower blade to stop. The first is a blade strike. A blade strike is when you hit something such as a root or rock. It can bend the blade or push it into the deck.
Another thing that will stop the blade quickly is a stick getting caught in the blade or something gets wound around it such as heavy wire, a dog run cable etc,.
The other problem is the bearings will seize up over time and especially if they need grease and they do not receive it during your routine maintenance.
Sticks can also land on top of the deck and get caught in the belt or the pulley, so be sure to check that area too.
All of these problems are fairly easy to fix and may require that the deck be removed. If this is something that you are not comfortable doing, visit our Locations page for a lawn mower repair shop near you.