Ninja blenders handle some foods better than others. I would check the instructions in the company's user manual to make sure that you are blending foods that the Ninja can handle. The size of the food chunks might be too big or too small. If your blended product is too thick, cut the food into smaller pieces. You might also try using different settings to achieve different food consistencies. For example, you could try blending on a higher setting for a shorter period of time. I hope this helps. Follow this link for more information: Ninja Professional NJ600 Troubleshooting
I would take out the screws and open up the blender to get a good look at the internal components.. There will be a circuit board behind the button display where you can check for anything that looks wrong. Check out the following link if you're still having trouble: Ninja Professional NJ600 Troubleshooting
The first thing I would try to do is press the red reset button on the outlet that the blender is plugged in to. If there is no red button for this outlet, look for other outlets near the outlet that your blender is plugged in to. Often times this reset button will restore the circuitry in your home and will allow you to blend again. Take a look at this page if you can't seem to get it working: Ninja Professional NJ600 Troubleshooting