If you're having trouble connecting to the Call of Duty: Modern Warfare, you should first check Call of Duty: Modern Warfare Server Status. If the status indicator for your platform is not green or an alert is present, you might encounter connectivity issues until service is restored and fully operational.

Clear the Cache of Your Console. Another common reason for the Call of Duty Modern Warfare Multiplayer not working error is the corrupted cache data. In this case, you can try clearing the cache files on your PC or console to fix the issue.