Thanks for playing !
To distract the guard you have to throw(left click, Right Trigger) one of your treasure not too far from them, and if their is a wall between them and the item they don't get distracted !
For the graphics : Resolution 1280x720 is bugged it deactivate the light rendering. You can put the game in windowed-Fullscreen and force it up a bit to 1600 or 1920 and it's back to what it's supposed to be.