RE unlocking - I recomend playing through again. You can do things differently, and it's pretty easy.
Anyway if you don't want to - case sensitivity means that it tells the difference between capital and lower-case letters. Ie: hEllo, HELLo, HellO and HELLO are all different. So if the cheat was "LuKaS" and you entered "lukas" it wouldn't work.
So some Google turned up "J8OL14FD". Just type it in exactly as you see it there.