Please Help!

[JNolan92]

A few months ago, I ordered Amnesia: The Dark Descent from GameFly and everything was running perfectly fine. The other day, I had to do a reinstall on my computer and when I reinstalled Amnesia and entered in the correct serial number and everything, the graphics were very dark, even the menu. I could not see the stone walls in game and only shadows and I could barely see the wooden doors. I did a system restore to early on in the day and when I went to start the game, the executable was missing. I re-pasted the Amnesia folder from my USB flash drive onto my PC and when I went to start up the game, I did not have to re-enter the serial number and the game was still dark and everything.
Is there some way to fix this? Please help!

EDIT: By the way, I'm running Windows XP