Sounds like a virus to me. What kind of formula are you trying to do?

Any type of formula. *When I click the f= on the toolbar, the install
program applicatoin window opens. *Then I have to close it , *which takes
several minutes, before I can get back to my math formula. *I usually only
happens once when using a spreadsheet. *I run regular virus scans and doubt
that is the problem. *

I've never even seen a window like that (hence my virus comment),
unless you mean a basic Windows Installer window. Maybe someone else
has. Can you tell what it is trying to install? If it is Excel/Office,
perhaps part of your install is messed up and a Remove and reinstall
might help.