To troubleshoot login issues on portal.office.com, ensure your internet connection is stable and the website is accessible. Verify your username and password, ensuring no typos or incorrect credentials. Clear your browser's cache and cookies, or try accessing the portal in incognito mode or using a different browser. Check for any service outages by visiting the Microsoft Service Status page. Ensure your account isn’t locked or blocked, and reset your password if necessary. If multi-factor authentication (MFA) is enabled, confirm you have the correct authentication method. Contact your IT administrator or Microsoft support for further assistance if issues persist.