Uploaded music in iTunes won't play or plays incorrect songs

On iTunes (whatever its now called) some of the tunes I previously up loaded will no longer play even though they are still showing. Some are my own recordings and I don't have any other copies so it is quite (very) annoying. Its only recently started happening. Others seem to be playing a different song altogether. I am not using Cloud as far as I am aware. Everything is (should be on my computer). Help?