Recently whenever I play a game, it runs perfectly normal then my monitor goes all:

Then:

Then I have to turn my computer off and on for it to stop.
then this happens:

Then it starts up fine and I open my game again, and the cycle repeats.
Games it has done this with:
Blockland
Warframe
I am running windows 7 on a Dell computer

is it my Monitor's fault or my PC's?