See that the blade is not obstructed.

If the device is not washed well between uses the blade can get a little caking underneath; try manually moving the blade (with a butter knife or chopstick) to get it going again. The blade can also lose lubrication if the device has not been used for a while; manually moving the blade before running the device can help start the motor.

Give the lid a good turn. 

It could be that the lid wasn’t turned far enough. People often stop when they feel it tighten but should continue to turn past the tight point until you feel it click.

On the other hand, you might be too strong for your own good(!) and closed the lid too far past the clicking point. Slightly open and close the lid a little bit to get it going.

Check that the electrical conductors aren't wet.

Ensure that the gold conductors on the inside lip of the bottle are not wet. Make sure the device is not too full of liquid—only filled to the fill line—overfilling could result in liquid hitting the conductors.

Pod problems.

A couple pod issues may be causing your blending woes:

First, make sure that you leave the pod in the device when you put the lid on. Do not empty the contents of the pod into the device and discard the pod. The pod's presence is part of what makes the blender run.

Second, be sure that you have peeled the label off of the pod (that includes the clear seal, if there is one).

Too much liquid.

Too much liquid in the blender can prevent the pod lid from fully opening, trapping some powder and preventing a complete blend. Be sure to fill the blender just to the fill line.

Hardening of the blend powder.

If you notice your blends have hardened, this is due to the organic sugars found in real fruit. Rest assured, this is the result of natural processes and does not compromise the quality of your blend. Try giving the pod a gentle pinch and shake, then proceed with blending.