The JS files are automatically loaded within the zencart format. It is definitely a JS issue as long as you upload the files located in the folder includes > templates > your_template > jscript they will automatically load.
Another issue if you have any other JS on your page or in that folder I have seen them interfere and not work. Without having access to your files its hard to find the exact source why its not working.
I would first make sure the files are all uploaded as given
check for any other JS files on the page
What template are you using if you dont mind me asking?
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