There is a problem sometimes with the performance/stability of the Relational Database Courses however.
It can sometimes take up to several minutes on that screen before the course fully loads.
If it seems completely stuck however, you can try keeping that tab open and opening a different course in another tab. This can help the original tab to get unstuck.
Or you can close the tab and try again.
For further information, there is a general troubleshooting guide (linked on the main page for these courses):