As the availability of 'new' unopened copies of FSX decreases it may be worth reminding people that there were actually three variants of the product / product update produced.
Original FSX had numerous faults 'out of the box' including showing 3D scenery as black outlines because of its inability to render textures correctly.
Original FSX must be patched in order to get the majority of add-ons working correctly. The correct way of doing this is as follows.
Install standard FSX and run a single flight. This will unpack all the files and build the libraries.
Download Service Packs 1 and 2 from Microsoft.
Service Pack 1 here: -
Service Pack 2 here:-
Install service pack 1 and again run a single flight. Close down FSX and Install service pack 2.
You will notice an increase in loading times even on a very modern computer. This is due to FSX now processing all the data it was supposed to process but didn't 'out of the box'.
If you have purchased Standard FSX plus the Acceleration expansion pack you should run FSX the once before installing Acceleration.
The Acceleration pack will give you service packs 1 and 2 combined plus some additional aircraft and scenery not included with the service pack downloads
Lastly if you have purchased FSX Gold then you have purchased FSX and Acceleration as a single package. Simply follow the install instructions that come with it.
Please also see the item on 'Must have files' to update another very important aspect of FSX.