The lid must be put on correctly. There is a plastic piece on the lid that pushes into the handle of the processor once turned. That in turn pushes the black lever down on the small button on the base. The small piece mentioned above being depressed by popsicle stick.
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=== Update (11/28/2019) ===
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https://youtu.be/i0T9NcpB0CU
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watch the video and fast forward to the time of 6:02 on the video. It shows how the piece pushes into the handle which depresses button on the base.
The lid must be put on correctly. There is a plastic piece on the lid that pushes into the handle of the processor once turned. That in turn pushes the black lever down on the small button on the base. The small piece mentioned above being depressed by popsicle stick.