Sign-in & Login Problems

Fix Microsoft 365 Copilot and Office Sign-In Error After Reinstallation

Amos Gikunda Sep 29, 2026 868 views

Question details

The user is unable to sign into Microsoft 365 or Copilot after reinstalling the Microsoft Office suite.

How to Fix Microsoft 365 Copilot and Office Sign-In Error After Reinstallation

Product: Microsoft 365, Copilot
Device & OS: Windows
Scenario: Attempting to log into an active Microsoft 365 or Copilot account following a fresh software reinstallation.
Observed behavior: The sign-in process fails and returns an error, typically caused by corrupted network connectivity, DNS resolution issues, or conflicting cached credentials.

Before you start

Ensure you are connected to a stable internet network and have administrator privileges on your Windows computer, as they are required to perform network reset commands.

Solution 1Recommended

Reset Windows Network Stack via Command Prompt

This is the most effective method to clear corrupted network configurations and flush DNS caches that may be blocking the connection to Microsoft's authentication servers.

Network connectivity issues or stale DNS records can often prevent desktop applications from verifying your account online. Running a series of reset commands will restore your network adapters to their default states.

Open Command Prompt as Administrator

Click the Start menu, type 'cmd' in the search bar, right-click on 'Command Prompt', and select 'Run as administrator'.

Reset the Winsock Catalog

Type 'netsh winsock reset' and press Enter. This will recover the computer from any socket errors.

Reset the TCP/IP Stack

Type 'netsh int ip reset' and press Enter to rewrite two registry keys used by the TCP/IP stack, restoring it to its original state.

Release, Renew, and Flush DNS

Run 'ipconfig /release' to release the current IP, 'ipconfig /renew' to request a new one, and 'ipconfig /flushdns' to clear the DNS resolver cache.

Reset Windows Network Stack via Command Prompt

Restart Required: You must restart your computer after executing these commands for the network resets to fully take effect before trying to sign in again.

Solution 2

Clear Stale Office Credentials and Verify System Time

Removing old saved passwords and ensuring your PC's clock is synced correctly can resolve authentication blockers.

Free Microsoft Office alternative

Try WPS Office: A Free, Lightweight Alternative to Microsoft 365

If you are tired of dealing with complex sign-in errors, connectivity bugs, or expensive subscriptions after reinstallations, WPS Office provides a hassle-free, powerful solution. It seamlessly handles Word, Excel, PowerPoint, and PDF files all in one lightweight application.

1. Download the Installer: Visit the official WPS Office website and click the free download button.
2. Install Quickly: Run the small installer package; it installs much faster than traditional office suites.
3. Open Your Files Instantly: Drag and drop your existing Microsoft Office files into WPS Office and start editing without needing a complex sign-in process.

Fully compatible with Microsoft Office formats like DOCX, XLSX, and PPTX.Lightweight installation that runs fast and bypasses complex network dependencies.Familiar and intuitive user interface requires zero learning curve.Completely free to use with robust built-in PDF editing and AI features.

microsoft office alternative - wps office

Frequently Asked Questions

Why does Microsoft 365 show a sign-in error only after I reinstall it?

Reinstalling Office can sometimes leave behind outdated registry keys, corrupted cached credentials, or misconfigured network settings that conflict with the fresh installation's new authentication requests.

Will running the network reset commands delete my saved Wi-Fi passwords?

No. Running the 'netsh' and 'ipconfig' commands will only reset your network adapters' configurations and flush the DNS cache. Your saved Wi-Fi networks and their passwords will remain intact.

What should I do if clearing credentials and resetting the network doesn't work?

Try connecting your computer to a different network, such as a mobile hotspot, to rule out router configurations or ISP-level blocking. If the issue persists, contact Microsoft Support and provide them with the exact error code shown on the sign-in screen.

Login & Account Issues