Basically, I can't change it, can't install nwn2. I see new users in proprieties/permissions, options to change permissions is greyed out. Possibly a virus?

Why are you installing games (or anything for that matter) into program files? Never, ever install anything into folders owned by windows, it is half the reason things don't work. Create separate folders like c:/mugames, and install your items there, thus avoiding UAC issues.

Next question, why do you need to change permissions?

Because I have no permission and new users on my computer. (Creator owner and trustedinstaller)

??

You have no permissions on your own computer? How did you install it in the first place?

I had permissions, but now I have no permions for my user and I see new users which I did see before.

What is "program filesx84"? A typo, or is there really now such directory in your file system and you can't change its permissions?

Maybe malware? Who knows? Maybe you should restore to an earlier restore point, or maybe even reset your Windows installation?

I am sorry, you have lost me. When you logon to windows, you have a profile. This is either admin or user. Depending on what the accounts are setup, admin can always install and change things. User tends to be more restrictive. So when you start windows, login as admin. Then install your game preferably outside windows folders, and make it available to all users. It sounds like you have logged in as a user with limited privileges, but without knowing anything about the setup it's hard to say. Does someone else admin your system?

Do you mean you're seeing new users, which your didn't see before?

Correct.