1; Yesterday I updated and refreshed my personal web sites using NOF 2015
2; Decided to then clean up my Windows 10 PC and removed NOF Versions 12 and 2013 that had been sitting unused since August 2015, when I upgraded to NOF 2015
3; Today I turned on PC and went to open NOF 2015 and got an error message: "The serial number entered for this installation is invalid. Please obtain the serial number from your registration card and reinstall or contact customer service."
4; So now I don't have an earlier version of NOF on the PC and the program will not open NOF 2015 which I have been using for three years
5; I have been a low end user of NOF since late 1990's for my own personal web sites (4).
6; I have my serial numbers for NOF versions 2, 4, 5, 6, 7, 11, 12, 2013 & 2015. NOF versions 7, 11, 12, 2013 & 2015 are all upgrade serial numbers, but not sure about the earlier versions
7; I originally downloaded the NOF 2015 upgrade from NOF website and don't have a disc with the program

Please, can someone explain how to get NOF 2015 working again, without losing any of my latest 2015 USER websites.
PS: I am thinking of buying a new computer this year, how will I get NOF 2015 onto that PC?

With thanks,
Melbourne, Australia