Note that this is not a question about the Unreal Engine itself, but related to games made with the Unreal Engine.
A week ago, all of the Borderlands Games stopped reacting to my mouse. I could move it around and click all I wanted, for the games it didnt exist. Initially I contacted the game’s publisher, but it has been a week and no solution has been found. Since then, I have tried other games from different publishers that were made with the Unreal Engine (or at least powered by), and the same problem happens there. So I concluded that it may be related to the engine, not so much the games themselves.
Incidentally, using the Unreal Engine itself is not a problem.
I use Windows 8 (8.1? not sure), but all games worked before that moment when they stopped working. It may be due to a windows update, but it may also not be.
All in all, not being able to use your mouse in FPS games renders them unplayable, so anyone who might know a solution is welcome!