Reinstalling Mathcad 14 after a hard drive crash

My hard drive crashed, recently, on my Win XP-Pro PC. I have reinstalled Windows and most other programs. When I try to install Matchcad 14 I get a message that I do not have a previous version of Mathcad on this PC (my Mathcad 14 disc is an upgrade disc). I have been a Mathcad user since almost the beginning of Mathcad. Every version of Mathcad that I still have is an upgrade from a previous version, therefore I can't install a previous version so I can then install my MCAD 14 upgrade. How do I fix this problem?