If you are going to do web development you need to acquire some basic skills and strategy for solving such problems.
Think about the problem and how to find out what is happening.
Any experienced web developer would start by doing the following:
- View the source of the page
- using browser dev tools to see if there are any script errors happening on the page or the network tab in browser tools can show if any files are failing to load (ie in Chrome right click > Inspect Element > Console will show if any script errors are happening)
Hope that helps,