iPod function does not work. Other sound app's do.

Every time I try to put on a song on my iPhone, it screen jumps from the listview to the 'playing song'-view as it's supposed to, but then the play-icon in the upper right corner of the screen starts flashing, and after about 2 seconds, it jumps back to the list-view, without playing playing the song.

It does not matter if the headset is connected or not. Trying to start the music with the button on the headset also does not work (also the flashing play-icon thing).(So most probably it's not the headsetconnecter.

Other apps that produce sound, such as games or the YouTube app do work properly.

Soft resets / reboots don't work..

Does anybody have an idea what it could be? Maybe a defect to the dockconnecter of headphoneconnecter?

Thanks in advance!