Please ensure the .xls file is not opened in other workbooks, add-ins, or apps. After coming to that conclusion, simply attempt to open the file again in Excel to see if the problem no longer exists.

If the two Excel workbooks have the same name, you cannot open them at the same time. For this, either close one of them and then open the other or change the name of one of them.

When you first installed Microsoft Excel, it should have registered itself as the default program for opening compatible file types, such as .xlsx or .xls. Installing other spreadsheet programs ...

Microsoft Excel has several features designed to help you recover unsaved versions of files and prevent data loss.