I had no idea how to play the song. I was jumping, jumping, jumping and hitting "enter" in front of the instrument, and nothing happened. Took me ages to figure out that I need to use the mouse.
If nothing happens, then probably you did not play the song correctly.
what Sororia Rose said, click them with the mouse, one note at a time, the same tune. the further you go the more notes you have to play. the final stage has 11-12 or something, took me two tries.
It's a bit like Simon the game. If you can watch the notes and listen fine but if you can't, figure out which buttons correspond to which notes on the wall. You are given the notes on the staff (the lines) and then just match up which buttons go to which notes. It might take 2 tries or so or may need to be written down by some, but not an insurmountable quest.
There's a small "Play" button which will make the ghost of Esquibeth repeat the sequence. Very handy for the latter stages if you're as non-musical as me.
I had no trouble figuring out what I was supposed to do, however I did have trouble remembering exactly *what I'd heard, in the end I switched off the sound, and figured out the sequence by using the visual clues.