Here are the steps you should take to troubleshoot this issue:

1. Check your internet connection: Make sure you are connected to the internet and that your internet is working properly.
2. Disable your pop-up blocker: Pop-up blockers can sometimes interfere with Microsoft Classroom.
3. Clear your browser’s cache: Clearing your browser’s cache can often help resolve issues with Microsoft Classroom.
4. Enable JavaScript: JavaScript is used by many Microsoft Classroom features and must be enabled for it to work correctly.
5. Check your browser compatibility: Make sure your browser is compatible with Microsoft Classroom.
6. Contact Microsoft Support: If you have taken all the necessary steps and you are still having trouble, you should contact Microsoft Support for help.