Amnesia help please :(((

[swornxin]

i bought Amnesia: The Dark Descent last year and played it on my PC for a few months yeah yay fun memories whatever

so i just got a new laptop and i wanted to play it on here.
everything is installed, then a serial number box pops up (asking for one)

im assuming the serial number was on the case and i threw it away not even thinking one day im sure.
so i dont have it anymore.

I have the disk and all the numbers on that, i think i even have proof of purchase.

someone either help me or kill me
i dont want to waste money on buying it again when the game is installed in my computer and whats holding me back from descending into the darkness of amnesia is a misplaced serial number.

someone help me please, like as soon as possible.
im mad