Looking at the image you sent to me via email, you can see the NAV / GPS on the switch, but it is "merged" with MARKER HIGH / LOW texture. I can only assume that it is either a graphics error, or a setting in FSX is causing the background texture for NAV / GPS to be semi-transparent.

Reinstall the csp721_2700.exe, and use the "Repair" option when given the choice to Repair or Remove. Make sure you turn OFF your AV, and Windows Defender, and that you run the installer using the "Run as administrator" option (right click on the installer, and select "Run as administrator" from the list (2nd from the top)).

By reinstalling the 727-100, you will reinstall all the VC textures (along with everything else for the 727-100), and hopefully it will correct the issue with the NAV/GPS switch. Reinstalling will also overwrite the aircraft.cfg, so if you have any added liveries, you will need to re-add them, or you can backup the current aircraft.cfg prior to the reinstall/repair. Do not replace the original aircraft.cfg after the reinstall/repair, until after you have checked to see if the NAV/GPS problem is fixed!