Diagnosis
The control board is stuck in a power-on self-test (POST) error loop. This is almost always because the pitcher isn't seated correctly or the lid interlock isn't engaged.
How to Fix It
Unplug the blender base. Take the pitcher completely off. Look at the black plastic drive socket on the bottom—make sure it's clean and dry. Align the pitcher's drive socket over the metal drive stud on the base and press down firmly until you feel a solid click. Then, plug the base back in. The lights should stop flashing and settle on the last used speed.
If That Didn't Work
Check the clear plastic lid. There's a small tab on the lid that must slide under the metal latch on the pitcher handle. If it's not fully locked, the safety interlock prevents operation. Push the lid down and slide it back until it clicks under that latch.
Heads Up
If the lights keep flashing after a perfect seat and lid lock, there's a chance the control board itself has failed, which requires a warranty call. Don't try to run it with the flashing error—it won't engage the motor.