Delete the entire Dying Light Documents folder, please:
Having done that, go to your Steam LIBRARY, right-click Dying Light, select Properties, open the Local Files tab and select VERIFY INTEGRITY OF GAME CACHE, please:
If the issue persists, perform the steps below, please:
If your devices (video card, CPU) are over-clocked, set them to their defaults.
Re-install your video drivers (with a clean install option, if available).
Close all unnecessary applications working in the background before running the game.
Try re-installing the Game on the default hard-drive of your PC (not an external one).