Please could somebody help?

I am a newly qualified teacher and I have trouble with one student - they always put there head on the desk and don’t do any work. What could this mean, does this mean there upset?

When I asked them ā€˜Whats a matter?’, They answered with ā€˜it doesn’t matter.’ So I’m really not sure what is wrong with them or what I can do next.

Please someone answer.