Diagnosis
This is almost always a power supply issue. The motor is trying to draw more current than your outlet or extension cord can provide, causing it to bog down.
How to Fix It
First, unplug the blender. 1) Check that you're using the correct voltage for your country (it's a 120V motor). 2) Plug the blender directly into a wall outlet, not a power strip, multi-plug adapter, or extension cord. These can't handle the high initial power draw. 3) Make sure you haven't overfilled the pitcher—don't go above the MAX line, especially for thicker mixtures.
If That Didn't Work
If the problem persists even in a direct outlet, try blending something much lighter like just water. If it still struggles, there might be a fault in the motor's thermal protection or the power cord itself, and you should contact Cuisinart support.
Heads Up
Never use an extension cord with this blender, even a "heavy duty" one. specifically warns against it because the motor's startup surge is substantial and needs a direct, high-quality connection.