Computer registers as different machines

A couple of times already, when asking for a reactivation for a limited activation on some software, I get told I installed the software on different computers, which is not the case. I've got only one computer on which I run my flightsim software, which hasnt been changed in any way, but somehow it registers as a different computer than it did the last time I activated some software and this happens every time Windows is reinstalled.

Does anyone know what might be causing this?

System Specs:

Asus Z87k

Intel i7 4770-k

MSI GTX770 4GB

Corsair Vengeance 2133Mhz 8GB

Kingston SSDNOW 200 SSD

Crucial MX100 SSD

Windows7 Home Edition 64-bit