Diagnosis
The motor is jammed. The most common cause is something thick like frozen fruit or nut butter stalling the blade assembly.
How to Fix It
Unplug the blender immediately. Remove the container from the base. Use the tamper through the lid opening to manually rotate the blades counter-clockwise to free them. Add more liquid to the recipe, replug, and start on the lowest speed.
If That Didn't Work
Check for a seized bearing in the blade assembly. Remove the container and see if the blades turn freely by hand. If they're stiff or gritty, the container needs replacement.
Heads Up
Never run the motor stalled for more than a few seconds. It can overheat and trip the thermal protector, requiring a long cool-down. Always use the tamper with the machine running for thick blends.