What to do when the screen go black when playing team fortress 2

close the game with task mamager then, then re-open it.

This could be an issue with video card drivers, applciations running in the background, or a variety of other issues.

Restart your machine and let the desktop start normally.
Close any autorun programs, like torrents or any other file sharing.
Run TF2.
How long before the screen goes black? Does the game stop? do you still have sound?
Are your video card rivers up to date?

good luck