Go to any Office app and ensure you’re signed in with the same Microsoft account linked to your license. Remove and re-add your account under the "Account" settings of the app if needed. If this doesn’t work, reset the credentials in your Windows Credential Manager resolve Outlook not sending emails fast or contact Microsoft support for further assistance. Despite its robust feature set and user-friendly design, it’s not uncommon for end users and IT professionals to encounter sign-in and activation issues. If you or your employees can’t sign in to Office 365, or if the applications repeatedly prompt for activation, productivity can grind to a halt. Yes, Microsoft 365 works offline for most apps like Word and Excel.

How do I fix the ‘Product Activation Failed’ error in Microsoft 365?

By verifying the basics—correct credentials, valid license assignments, and stable network access—you’ll often fix the issue without delving into more complex solutions. Clearing cached credentials, running a repair, or using the Microsoft Support and Recovery Assistant (SaRA) can also address common local device issues. Verify that you’re logged into Outlook Stuck on Synchronizing Folders the correct Microsoft account both in OneDrive and Office apps. If syncing is paused, resume it from the OneDrive system tray icon.

Recover your account

Office 365 uses several internet endpoints and cloud services to authenticate users and validate licenses. If these connections are disrupted, sign-in and activation will fail. Use the Excel check troubleshooter to resolve Excel for Windows startup, hang, or crash issues. Get Help has troubleshooters for Microsoft 365 you can run for many common scenarios. These often help resolve issues without the need to contact support. If a troubleshooter is available for your issue, select Start to run that troubleshooter.

3 Step 3: Verify Network Connectivity and Firewall Settings

• If you or your employees can’t sign in to Office 365, or if the applications repeatedly prompt for activation, productivity can grind to a halt.
• For syncing or email issues, verify your mobile connection or switch between WiFi and cellular data.
• By verifying the basics—correct credentials, valid license assignments, and stable network access—you’ll often fix the issue without delving into more complex solutions.
• Larger files may cause a temporary slowdown, so ensure your device has adequate memory.
• Slow performance can be due to heavy CPU usage or low available memory.
• If your account is locked due to multiple unsuccessful login attempts, wait for the lockout period to end.
• In many cases, performing simple checks—like verifying correct usernames and valid licensing—will resolve the issue quickly.

You might find it simple, but the most common cause of login failure is entering the wrong username and password combinations. Below is a structured approach to diagnosing and resolving Office 365 sign-in or activation errors. Start with the basics and move toward more advanced methods only if necessary.

Microsoft 365 Troubleshooting – Quick Fixes for Common Problems

Use the Microsoft 365 activation troubleshooter to resolve Microsoft 365 subscription activation issues. Slow performance repair corrupted OST in Outlook can be due to heavy CPU usage or low available memory. Close unused tabs, background processes, or applications to free up system resources.