This is a known issue. I am assuming you are trying to start the System Architect Essentials course as you have not included it in your post. You can try again to see if it is up and running. In the meantime you can also download a virtual machine from the course under Completing the exercises lessons in the first module. Please make sure to follow the Virtual Machine User Guide to set up the first machine properly.

Sean
Pega Academy Self-Study Support Team