Well, start with looking if inside the scenery library everything is alright and selected. If the activation tips near the various scenery calls are absent, reactivate them yourself then restart FS and see it it works.
If inside the scenery library everything looks OK, then you have a problem. And a problem I've never heard of before.
If worse comes to worst you might need to reinstall.
Free downloads of add-on planes and scenery you can find here on
SimV, or
AVsim, or
FlightsimCom, or the less known
World Serious Pilots, and even others I don't remember at the moment.
Note that to download from AVsim or FligtsimCom you must subscribe (free) and login first.
There's but one real cure for human stupidity. It's called DEATH.
At the moment mourning the assassination of sarcasm and irony for the good of the "higher".
Proud FSIX user. Active user of FS98, X-plane and novic