If there is not a flaw in the product itself it could be a problem with assembly or that the locking bar is not locked in place properly. The juicer will not operate if the locking bar does not click in to place in to the grooves on both sides of the lid.
Jack LaLanne has several HowTo videos posted that would be worth reviewing:http://www.powerjuicer.com/power-juicer-how-to-videos.php
You are also able to download a manual which includes illustrated assembly and disassembly instructions:http://www.powerjuicer.com/power-juicer-manuals.php
If you are unable to lock the locking bar in place it suggests that some other component has not been installed in the correct position. Review the assembly instructions to make sure all pieces are properly positioned.
Thank you for using FixYa!