If so, what should I move or delete within REGEDIT as I have never used it before for anything.
The correct situation
with ONLY FSX:SE installed is to have the FSX:SE\10.0 key
REMOVED:
HKEY_CURRENT_USER\Software\Microsoft\Microsoft Games\Flight Simulator - Steam Edition\
10.0 ONLY the "10.0" should be removed!
And the FSX registry key:
HKEY_CURRENT_USER\Software\Microsoft\Microsoft Games\Flight Simulator\10.0
Pointing to the FSX:SE installation folder. This is a CORRECT registry
for an FSX:SE installed with no FSXAnd, be sure the "Co-existence" key in the FSX:SE registry folder, is set to 0.
AFTER you fix your registry, reinstall GSX.