can't import songs from computer to itunes!

I am unable to add music files to my itunes library. If I click the 'add file to folder', i get the message that the file is not in the wma format and will be converted by itunes. but nothing happens, and the file isn't added. i've alternatively tried dragging files into itunes, but i just cannot seem to add music to my itunes library unless by importing using audio cds.

Most of the songs are ones I have saved in my music folder, or else burned from a cd onto a different computer and i've saved them onto this computer. but itunes wont recognize them. thanks for your help!