No doubt of zswobbie1 solution. Maybe the allocation of the registry allows to run FS9 OK.
I have found a easy way to install FS9.
1- Create a new folder (where you want) and name it as you like.
Inside that folder create 4 folders an name them Disk1 to Disk4
2-Open each disk and copy the content in the corresponding Disk1 to Disk4 folders.
3- Go to Disk1 and execute installer. It installs the complete program without asking for the other disks.
4- Install SP1
For running FS9 in Win 10 you need to replace the FS9.exe with:
Microsoft Flight Simulator 2004 V9.1 No-CD Patch (search in google)
Run as Admin. and in compatibility mode: Win XP SP3
Also with Nvidia cards, use Nvidia inspector and in: 1-COMPATIBILITY - Antialising compatibility, select 0x004412C1 (Diablo III). If not selected, Antialiasing adjustments won't work.