Right I've found the fault and I've found the solution:
The fault: If you have an Intel i3, i5 or i7 then for some reason the game usually chooses your intergrated graphics card not your high-performance one,
The solution: Go to your desktop, right click, click on Nivida control panel. Then go on to manage 3D settings, then click add and find Crysis 3. Once you've found it and added it to the list, click on it and change it to High-performance Nvidia processor. Then go on the game and it should be absolutely fine!