We have some computers on which our Excel Addins will no longer work
the way they are supposed to. We have used the Excel setup to repair
Excel 2003, and to remove and re-install it, but to no avail.

The actual problems are too involved and obscure to explain here.

My question is: are there any other tools available to diagnose, check
and repair an Excel installation? Is there a guaranteed way of getting
back to square 1, short of formatting the hard drive and re-installing
Windows?