Original post by: Rany ,
Have you tried the original headphones (if you don't have them anymore, borrow them for the test)? If yes, and they work without pushing down hard, then it means everything else you're using is ill-fitted. If the original ones don't fit in properly, then it could mean that something's wrong with the headphones jack cable, and it needs replacement such as by following [guide|7281|thi guide] that has all the needed steps, tools, and parts. Note that that particular repair is a bit of a PIA.