When a course is frozen it is often a result of a file that did not download correctly, often due to an internet connectivity issue.
To correct this we have to delete the problematic file and re-download it by doing the following:
Clear your browser history (specifically any downloaded files)
Close your browser (depending on your setup some settings may only cleared when the browser is closed).
Log back in with your username and password
You should be able to pickup where you left off.
If this this does not solve the issue please confirm that you are using an approved browser to access the course