I have a problem finding the addon file.
FSX works quite well with a few black squares around airports.
I switched files from C to D drive as there was much more space in the D Drive.
Not sure what you mean by add-on file.
I'm guessing the airplane folder in the main FSX folder.
Type Microsoft or other key words in the white space (W10) next to the start button and the main folder should show up.
You always have problems when you use any other drive than "C".
The folders are scattered over two drives.
I had 100 k on the C drive and 900 on the D Drive! hence use of the larger drive.. Problems with Trainz sim as well.
Had FS working well 18 years ago and just getting back to simming now I have retired.
You'll enjoy it more now with a better computer.
Let us know how you do.