Weird Problem Steam doesn't recognize FSX:SE files

Hi. I am running Windows via bootcamp, so actually I'm using a Mac, and today when I tried to log in to Steam, in the Windows side, Steam said I was already running my profile in this computer. I just restarted Steam, logged in again, and everything went fine. But then I noticed my FSX was appearing as desinstalled in my Steam. I wasn't being able to play it at all, as Steam wasn't recognizing FSX files. I've checked the files and they're in their proper place.

 

The thing is, I am able to start FSX, but when I open the 'Free Flight' menu, the game crashes immediately, as it is being run through Steam and Steam doesn't know there the files are. I think that is the reason. At least I know that the game doesn't have any data because it's all inside the Steam/FSX folder.

 

And trying to initiate the install in Steam actually isn't a solution, as I don't have enough disk space available. There must be another way to make Steam recognize the files once again. A help would be hugely appreciated :)

You need to check the integrity of your files, from steam click library, right click flight sim steam edition, click properties, (TAB)-local files-verify integrity of files, that should fix any corrupt files.

Well problem is that Steam thinks the game isn't even installed, so I can't do things such as verify the integrity of files

As long as you try to re-install the game to the same location, Steam should see the existing files and won't download them again. It should verify and fix anything that may be missing.