Applications :: Itunes Not Playing Some Songs - Unable To Add Or Delete Folder

itunes has decided to go all wierd on me and started playing some of my songs but not playing others. When i try to play one that will not play i get the apple logo on the top of the screen where the amount of time your into the song is normally shown and no matter how many times i press play nothing happens.

Also the songs that won't play all are coming from the same folder and when i delete them and try to add them to the library nothing happens and they aren't added. When i try to play the songs from that folder using a program other than itunes the songs play fine.