If you close excel and restart it in Safe mode, does it still occur?

Close excel
windows start button|Run
excel /safe

Start typing in that new workbook--not a file that you open.

I'm guessing that you have a book.xlt template workbook in your XLStart folder
that has all the cells formatted as text.

If it works ok when you start in safe mode, then close excel and try this:

Use windows explorer and search for XLStart.
Move all the book.xlt (along with sheet.xlt) to a different (out of the way)
location.

Then try opening excel normally.  Start a new workbook to test it out.

If that works, you'll still have to fix any existing workbook--just format the
cells you want to change as General.

Neil

My next shot would have been basically what Dave P. has suggested.

I think the workbook/worksheet template you're using is formatted as text and
you should start over with the default File>New...>Blank Workbook that Excel
provides.

This default workbook is not based on the one you have in your XLSTART folder.

I am surprised however, that the "copy a blank cell formatted to General" does
not fix the formatting of the cells.

Gord