Rockstar Games has pulled the PC version GTA4 from Steam and Microsoft’s Games For Windows Live platform is partially to blame. No word yet on when Grand Theft Auto 4 will return to Steam.

Rockstar Games has pulled the PC version of Grand Theft Auto 4 from sale, as the developer addresses a technical issue with the game.
Grand Theft Auto 4 disappeared from Steam over the weekend the product page is still up, but customers cant purchase it because of its ties to Microsofts Games For Windows Live platform. According to a statement from Rockstar, Games For Windows Lives demise impacts how the game is sold through services like Steam.
Heres Rockstars statement, forwarded to Polygon:
Grand Theft Auto IV was originally created for the Games For Windows Live platform. With Microsoft no longer supporting Games For Windows Live, it is no longer possible to generate the additional keys needed to continue selling the current version of the game. We are looking at other options for distributing GTAIV for PC and will share more information as soon as we can.
Grand Theft Auto 4 was originally released on Windows PC in December 2008, the year after Microsoft launched Games For Windows Live alongside Shadowrun for PC and Xbox 360. Microsoft discontinued support for Games For Windows Live in 2014, leading many developers to update their games to remove hooks into the service.