Iphone 4 is not ringing anymore

when i move the top left corner switch back from silent, it stays silent and the up and down buttons on the side won't work.

I tried all the possibilites on settings and the demonstration sound for ringtones works but when somebody is calling, it stays silent.

i also tried resetting it, plugged in several times the earbuds (when they are in, the ringing works), and plugged it to itunes. It is still silent, also the keybord and lock screen do not sound.

help me please, thanks