all my excel spreadsheets disappear. this is the third time this happened.

I understand how concerning it must be to have your Excel spreadsheets disappear repeatedly, especially since this is the third occurrence. First, you need to determine whether the files have actually been deleted or are simply no longer appearing in Excel. Please open File Explorer > This PC and search for *.xlsx to locate Excel workbooks stored on your computer. Also, open Excel and check File > Open > Recent to see whether your missing workbooks are listed. If you previously saved them to OneDrive, sign in to https://onedrive.live.com using the Microsoft account associated with Excel, search for the missing files, and check the OneDrive Recycle Bin.

Since this has happened multiple times, identifying where the workbooks were originally saved is particularly important before making changes to Excel, OneDrive, or Windows. Could you clarify whether your spreadsheets disappear from Excel's Recent files list, from their actual folders in File Explorer, or from OneDrive? Also, does this happen after restarting your computer, opening Excel, or making changes to the files? Are you using Microsoft 365 Excel or a standalone Office version?