Problem with excel
Have you tried a simple restart of Excel and/or your computer? That would be my 1st recommendation. If that doesn't work, make sure the font formatting for the cells is correct (this seems simple but could be overlooked perhaps). If that doesn't work you may try to repair/reinstall Excel (use the Office disc).
Let me know if you need additional help or if that doesn't work. Any additional information you can provide would be very helpful though.
Best of luck!