Does your book.xlt have the 1st sheet hidden?

If you have a template workbook named book.xlt in your XLStart folder, then
maybe it is missing sheet1.

Hi,

Expanding on the two previous suggestions since you may not know where the default workbook is kept or how to modify it:

The default workbook, which is usually named Book.xlt is generally located in the C:\Program Files\Microsoft Office\Office 11\XLStart folder.  (note Office 11 is just one possibility depending on the version of Excel you are using.)  You can always do a window's search for XLStart.

Open the file in Excel using File, Open.  Modify the file as necessary - 1. Unhide Sheet1 if its hidden, 2. Add Sheet1 if it has been deleted.

There is one other possible cause of your problem - there could be a Workbook_Open macro that either hides or deletes sheet1 every time you open the file.  This could be located in the Book.xlt file, the Personal Macro Workbook, or some add-in.

Cheers,
Shane Devenshire
Microsoft Excel MVP