Electric mower hum but no start - Black & Decker Lawn Hog 18-Inch 12 Amp Electric Mulching Mower

If motor is frozen the electric start motor will hum and burn out if it cannot turn of the gas engine.

Something has the motor unable to turn. Do not turn on till you locate the source of the problem lest you burn it out.

Most electric motor problems are caused by the bearings failing. Before that happens it may get very stiff but stil turn. With the power off, and the blade still attached, try turning the blade at least half a turn. Is that possible? Any noises as you turn? Is it very stiff or fairly free? If you turn it several times you may find that putting it upright and connecting the power it may start turning again.
Let me know what you find.

Steve it sounds like the brushes located at the top of the motor. They need replacing.

Bad starter. The starter is not connecting with the ring gear.I put a new gear in my starter.

it sounds like to me that the starter pully is getting caught up on the worm gear ,this could be because of dirt or grass getting in the way make sure that no grass or dirt is around the worm gear

Motor brushes are wearing out.

If the mower drive belt is extremely loose the spring that holds it tight may have broken,check to see if it is broken before you replace the belt

possible broken armature & magnetic ring.mower need max repair.