Recording Program in game, not possible?

Hey all, or that special PC genius WHO is out there.

I tried recording  in game (BF3, Tomb Raider and what not), but the same problem arises everytime. The screen goes Black, the audio is still there, but not visual.

Some suggested that I "windowed" the game, which I don´t know what Means exactly. I´ve tried a Vidoe Editing program called  Camstudio, but it won´t work as intended.

Anyone, can you help me? What to do, or do you know software that allows me to record in game?

Kind regards