Activating an old (OEM) license?

Bellzemos said:

But isn't the N version meant for the European market? I need Serbian language.

The N editions don't contain any media player software. Don't you want windows media player?
Windows 7 Direct Download Links, Official Disk Images from Digital River
Serbian language isn't in the list.
Do you know someone who has WINDOWS 7 PROFESSIONAL X64 serbian language?
Any other WINDOWS 7 X64 edition in serbian language is fine as well.

The bootable disks can very easily be converted into universal installation media supporting all Windows 7 editions (except Enterprise). There's only a single file that needs to be removed on the DVD. The file named ei.cfg in the sources folder restricts the choice of Windows editions that can be installed with that particular DVD. To remove it, you can apply the ei.cfg Removal Utility very easily.

Can you get such a dvd?

The Key is specific to the edition (Std/K/N/E etc) and MUST be used with the appropriate media.

Yup - Unless the sticker has the extra code it's the standard edition

I think the N versions were because of the browser hassle with the EU.