A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
You can refer to AI’s response first, as it covers the common causes and the main troubleshooting steps when SharePoint suddenly becomes inaccessible or the site/content appears to be missing.
In addition, please try opening SharePoint in an InPrivate/Incognito browser window and sign in to https://www.microsoft365.com/ with your work or school account. Then check whether SharePoint can be accessed normally from there. This can help rule out an issue related to the current browser session or cached sign-in information.
If the issue persists, could you please provide the exact error message or error code shown when you try to access SharePoint?
It would also be helpful to confirm whether you can access other Microsoft 365 services, such as Outlook or OneDrive, with the same account, whether the issue affects all SharePoint sites or only one specific site, and whether other users in your organization are experiencing the same issue.
If possible, you can also share a screenshot of the error message, after removing any personal or sensitive information.
These details may help further narrow down whether the issue is related to the account/sign-in session, a particular SharePoint site, or the wider environment.