*.xlb is the file where excel stores changes to the toolbars.  It can get
corrupted and Gary's Student guessed that it was that corruption that was
causing the trouble for the original poster.

You can create a couple of templates (*.xlt in excel speak) that can be used as
the basis for new workbooks (and new worksheets in existing workbooks).

The first one is named book.xlt (file|saveas|Template (*.xlt)).

This is stored in your XLStart folder.  When you click the New icon on the
standard toolbar, you'll get a new workbook based on this template.

The second one is named sheet.xlt and is saved in the same location (XLStart
folder).

When you add a new worksheet to an existing workbook, you'll get a worksheet
based on this template.

(When I did mine, I really created a single sheet workbook and saved it as
book.xlt, then I just copied that book.xlt to sheet.xlt--all within my XLStart
folder.)