How to Open an XLS File in Excel. XLS files are Excel workbook files created in Excel 97 or Excel 2003. The 2007, 2010 and 2013 versions of the program use the XLSX format by default to save ...

For excel XLSX file types for Excel 2007 files, start with the step where you click on the "Advanced" button and repeat. You need to change these variables for both file types to correct the problem.

If your Excel files are opening in Notepad on Windows PC, here's how you can reset the settings to make .xls, .xlsx, etc files open in Excel.