Thanks for your question!
This is a common problem experienced by users.
One reason it might not turn on is that the safety locking arm is not engaged. If this is the case, you can engage the locking arm by snapping it into the two grooves on either side of the juicer cover. Once it is securely fixed in the vertical position, you should be able to turn the juicer on.
Hope this helps! If you are still having difficulties, check out the [[Breville JE98XL Juice Fountain Plus Troubleshooting|troubleshooting page]] for other possible solutions.