Try to boot in safe mode and check that problem is occurring again or not.
My Nexus 7 is misbehaving; screens can't 'hold'.
I'll be in the middle of something, and the screen
disappears. Is that a memory problem or graphics?
I uninstalled Utube and have antivirus and antimalware
and system is Kitkat.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic