I have tried your code and it works just fine(menu is hidden).
Only differences are that I used jquery from my machine(You can cross check your jquery file validity using @Andy Lang's suggestion) and your header image is missing(I guess that's in your local folder)
If it still did not work for you, please open the developer tool in your browser and look for logged errors/messages in your console.
For example: If you get the below error, it means that you have not defined Jquery.
Uncaught ReferenceError: $ is not defined
If the error messages doesn't help, please post them here. We will help you solve it.
Note: Best practices involve declaring the scripts you need in the head section(just like you have declared your css file) unless you have a specific need to declare them in any other part of the file.