iTunes won't import .aac file!

I had a few files i wanted to import into my Library, and after try 'drag-n-drop' and 'import folder' methods iTunes would not respond. at first i thought this might be because it was a .flac file so i converted it to .aac, which filetype i know works with itunes. the file will open in quicktime, so i know they are not corrupt, but i can't figure a way to import them so i can use them.