DIAGNOSIS The motor thermal protector is tripping. This is a safety feature from excessive load or continuous run time.
FIX Let the blender cool down completely, at least 30-45 minutes. For future blends, use the pulse function more and continuous run less. For thick mixtures like nut butter, run in 60-90 second bursts with cooling breaks.
IF THAT DIDN'T WORK If it trips after very short cycles on normal tasks, the motor cooling fan may be obstructed by debris or have failed. The fan is part of the motor assembly.
HEADS UP Repeatedly tripping the thermal cut-off can weaken it. If it starts happening constantly, the motor assembly may need replacement.