If you are getting a blank white screen when trying to launch the course, right click on the right screen and select the option "reload frame". You may need to do this more than once before the cache is significantly cleared enough in order to display the course.
If the problem persists, you can try clearing your browsers cache by following the instructions here: refreshyourcache.com.
Depending on the settings you have enabled or disabled on your browser, it may be a good idea to try a completely different browser, like Google Chrome, or Mozilla Firefox.