All my FPS Game's minmize

[BigBig5]

Hi, when ever I play a FPS game it minmize about 10-20mins in to playing. I can't get them back to full screen most of the time, when I do they run super slow and they lag a lot.
The games are Urban Terror and Nexuiz. Does anyone know whats why they are doing that.

[Bölvaður]

turn off screensaver?

if it continues run the game from terminal to see the output when it gets slower, must be some error messages.

[Chemical Imbalance]

Yeah, check your screensaver settings.

[BigBig5]

I did that, so i hope it wont do that anymore.