This is assuming you have all the updates for NWN that are gained by running the update feature.
The first you always look at is...the video card. IF there is one.
If you do, check for updated drivers....then run NWN and get into the Video options and see if you attempting to run options that can degrade performance.
Another item to look at is the page file....the amount of you HD that is used as a "virtual" memory swapping area. If teh computer was bought as a package, this should not be an issue.
Last but not least is the actual memory on the computer....I have encountered one instance where the person had the MIN amount of mem to run the Operating system, let alone games.
Memory can be cheap if you not trying to max out...*As I do*
Give it a shot...there is little more can add without a serious amount of information.