Am running itunes 11.0.4 and not able to open either wav file or mp3 ?

Ok, so as someone who has been using Macs for a very long time and making music and the rest, I have suddenly found that I can't open a file for a backing track that has been sent to me using .wav format and now .mp3 - the files wont open in itunes (or show up in itunes) after I have tried adding to library and have even tried adding to my drop box and listening but NOTHING! Have checked settings and preferences and have mp3 decoder in drop down menu and have also turned off 'itunes match' incase that caused a conflict of some sort.

Am totally bemused.

Any advice from anyone?