Check you are using an up-to-date web browser as this may be the reason. 95% of training issues are caused by web browsers. Always make sure your browser is up-to-date before taking a training course.
Psittacus recommend Google Chrome which can be downloaded here: https://www.google.com/intl/en_uk/chrome/browser/desktop/index.html
You might have difficulties if your browser doesn’t support HTML5 or if you’ve got a cache build-up. It’s always worth clearing your cache if you’re experiencing problems.
The cache is a build-up of data in your browser. Different browsers each have their own ways to clear the cache. Copy and paste this link into your search bar to find out how to clear the cache in whichever browser you’re using: https://kb.iu.edu/d/ahic