I am not able to import wma files into library.

I have the macbook pro and itunes. when i add files from my harddrive -wma files , there is no change in the screen- nothing gets added to the library. Mp3 gets added. My import settings for cd are set in convert to aac files. I am not copying files added to ipod again to storage. I am using my hard drive as the location for itunes media files .