Diagnosis
The thermal overload protector is tripping. The motor is getting too hot too fast. This is often due to overloading the jar or a ventilation blockage.
How to Fix It
Let the base cool down for 30 minutes. Check that the base vents on the sides are not covered by a countertop lip or towels. When blending, do not fill the jar past the 6-cup mark for thick mixtures like nut butter. Use the Pulse function for heavy tasks.
If That Didn't Work
The jar might not be fully seated and locked. The safety interlock is disengaging. Remove the jar, align the arrows, and push down firmly until you hear a distinct click. The motor will not run without this lock engaged.
Heads Up
The motor has a cooldown cycle. If it stops, it will not restart until the internal temperature drops, even if you unplug and replug it. Wait it out.