Pause/Play and down volume buttons not working...

It started yesterday afternoon, it was working well in the morning but I’m not sure the cause of it if I acciendently dropped it (though I didn’t dropped it any time of the day as far as I recall) or was it the rain the day before (but it was off completely, not stand by mode or on). Any ideas on how to fix it? I was thinking of opening it and see the working inside and repair any of it but I don’t know how to open it without trying to break it. Any suggesstions? Thanks in advance.