The Steam version is no longer supported. You can either install the Games for Windows Marketplace version in order to play, or use a Steam URL to play.
Although the Steam version is no longer supported, the game can still be downloaded and played through Steam for the existing owners. If you activated any DLC for the game on Steam in the past, the entry should appear in your library, allowing to install the game. However, if you haven't purchased the game, you can still install the game using Steam's install URL:
There may be issues with activating CD-keys for DLCs bought previously from Steam Store. Contacting Microsoft Flight support directly by sending a mail to firstname.lastname@example.org describing the problem might help solving some of the issues.
Some users have reported an issue revolving around the Games for Windows Live client packaged with the game. Upon startup they are presented with the following error:
Games for Windows - LIVE filed to reinitialize.
Another Games for Windows-LIVE title may be running, or your product installation may be corrupted.
You may need to repair or install Microsoft Flight.(800b0100)
There is a simple way to fix it: You should uninstall Games for Windows - LIVE through Uninstall or change a program application, then download an install it again.
Some users have reported success by following the steps provided on the Microsoft support website. The catroot method often produces the best results for affected users. It can be conducted as follows:
net stop cryptsvc
ren %WINDIR%\system32\catroot2 catroot2_renamed
net start cryptsvc
The game may launch with a black window on-top of game window, obscuring the view and making the game impossible to play. The issue happened on Windows 8.1 64-bit with two monitors (1920x1080 and 1280x1024).