Airxonix was built for Windows 98/XP. If you are on , the registration window might crash when you try to type.
Finding an Airxonix Registration Key: A Complete Guide to Reviving the Classic Airxonix Registration Key
Right-click the Airxonix icon, go to Properties > Compatibility , and set it to "Run this program in compatibility mode for Windows XP (Service Pack 3)." Also, check "Run as Administrator." Name vs. Code Airxonix was built for Windows 98/XP
Frequent pop-ups asking you to register the software. go to Properties > Compatibility