I have already requested the cd key and extracted it into nwn. I have tried restarting my computer too. Nothing has worked so far. dont kno what to do

had the same problem. if you have the key on hand, just enter it into the .ini file in your nwn directory...the notepad should be called nwncdkey.ini or something like that.

1. is nwn core

2. is sou

3. is hotu

Did your install already have a nwn folder ?

I read another post that sugested that the install directory for gog version is differant then the one from the disk. If your nwmain.exe is not in the nwn foulder where you placed your CD-keys you placed them in the wrong place. The thread I read gave me the inpresion that thy should go in.
C:\Program Files (x86)\GOG.com\Neverwinter Nights Diamond Edition\

Since I do not own the GoG version I can only speculate here.

EDIT; If you have a desktop short cut to run the game. Right-click on it an select propteries. In the windo that opens click the 'Find Target' button. the folder that opens is the folder you should place your keys in.