Perhaps you need to edit the artist specifics. Sometimes i have to do this as songs by the same artist / band get catogarised differently. i.e. rock, alternative or indie.
also check spellings of the artist for example sometimes itunes will import them as The Beatles and also just Beatles.
Highlight all the songs effected (holding shift or Ctrl) and right click and enter the correct details into the boxes, and also click the 'sorting' tab and input the artist name in the 'sort artist' box you want them soring as. for example I have put 'Beatles' in this box fot 'The Beatles' so that itunes sorts tem under B instead of T.