Excel 2003 Data in Cell not Displaying

I have a user who is trying to enter data into an Excel 2003 spreadsheet created by a co-worker who is out of town and can’t be reached. When the user enters data into a cell, he sees the data displayed in the Formula bar, but the cell remains blank; the data never shows up in the cell. You can click on the “blank” cell and see the data in the Formula bar, though. As a work-around, he copies data from another cell into that cell first, and can then edits the data. Does anyone know why this is happening? I have tried googling this but haven’t found anything helpful yet. TIA…