The ESC button wont open in game. In the snapshot, single and multiplayer.

The esc button won't pause my game.

What I expected to happen was...:
I expected my game to be paused so I can access the pause menu and change some of the game settings.

What actually happened was...:
My game was still live.

Steps to Reproduce:
1. Load game and press the esc button.
I have also been unable to open the F3 menu and unable to change my perspective with the F5 button. Please help!