While working in Excel yesterday, I repeatedly got an error message every time i moved within the worksheet. I decided to un-install and re-install after nothing else seemed to work to correct the problem. I use the microsoft office student and teacher edition 2003. The un-install went fine but, when I reinstalled it keeps telling me there is aproblem with my product serial number. It posts this before I even get a chance to enter the product number! I don't know what to do to. Any ideas??? My operating system is Windows XP 2003.