Sorry for the late answer.
Ok so here are some basic instructions. We're going to check if the FSX path is registered correctly in the registry. Most 3rd party programs will read the registry to see where FSX is.
Go to your Start menu.
In the search zone, type "regedit" and press ENTER key
The registry editor appears. Be very carefull what you do from now, as deleting anything could lead to catastrophic results

The window has two part: a "tree" structure on the left, and an empty space on the right.
In the left part, expand the node HKEY_CURRENT_USER
Then go to Software
Then Microsoft
Then Microsoft Games
Then Fliht Simulator
And finaly, click on 10.0
In the right side, a set of lines appear. One of them starts with "AppPath". This is the install path of FSX, that is read by third party install programs. Check if this path is correct for your computer.