Hope you forgive a repost - like me, I've read lots of people playing Amnesia on a ATI Mobility card (like my Asus G73JH laptop with HD5870 card) has the computer freeze within seconds of starting the game - often a black or grey screen, sometimes with vertical stripes.
I managed to solve this today for me using this guide by Gary Key.
http://forum.notebookreview.com/asus-gam...blues.html
Turns out it is not the fault of Frictional, it is the firmware on the graphics card.
If someone else can verify that it works for them, perhaps you could add it to the guide?