- Restart your computer and then try to open OneNote
- Make sure you have the latest version of OneNote installed on your Mac
- Check the System Requirements for OneNote on Mac
- Verify MacOS settings are up-to-date
- Try rebooting your router if you're connected to the Internet by Wi-Fi
- Temporarily disable your Mac’s firewall settings
- Run an anti-malware scan on your computer
- Check your AppleCare support plan for additional help
