Headphone Jack Not Working Properly

Hi
I have a 2nd generation iPod touch. The headphone jack has not worked properly for a while now but it has been fine with my earphones. When I use an aux cable, I have to move the cable around to get any sound.

A couple of days ago, the earphones that I regularly use and anything that worked does not any more. When listening to music, I can hear the tune but not the singer or any beats. When I pull the cable out a little, I can hear everything and it is all working fine.

The problem started after I lent it to my friend. I went to plug my earphones it and I realised the black plastic around the headphone jack does not stick out has much as it did before.

Does anybody know how to fix this problem?

Thanks