Framerate issues with Amnesia: The Dark Descent

[AdamAK]

EDIT: Terribly sorry! I accidentally posted the thread in the Penumbra forum, rather than the Amnesia forum. Could a kind moderator please move it to the correct section?
Hello everyone,

It's been many months now since I have bought Amnesia, and I've had dozens of hours of fun with it. A few months ago, however, the game started running terribly. Regardless of what settings I use the framerate is dreadful, and the game is practically unplayable. I have not made any adjustments to my computer over the past few months, and this issue arose quite suddenly. I have tried things like updating my GPU drivers, and have even rolled back to the original ones now as well, but nothing seems to make a difference. No important software or hardware changes have been made since I've been playing Amnesia; just a few games being installed and such.

The odd thing is thus that I used to be able to play this game on high settings while streaming it while getting a solid 40/50+ fps, and now I'm getting sub 15 fps on the lowest settings without even streaming it.

Any ideas on what could be causing it?

I'm attaching a dxdiag file, but in short, my specs are:
i7-2630QM
4GB DDR3 RAM
Nvidia GeForce GT540M

EDIT2: Added the hpl.log file.