Can you share the configuration of the configurable product to show that there are associated products? Are the associated products all enabled in the same website with stock? Are there any console errors on the page?
This Is Console Error While Clicking On Drop down..
Looks like there is a problem here.
Firstly it complains of failing to execute a script. Are you able to tell from the network tab which JS file is failing to be loaded and why? If you can visit the URL directly, what do you see, is it a Magento error?