Sound in only one channel
 

My mp4 player only plays sound in the left channel now, but if I slightly tilt the plug in the headphone jack it plays in both channels again (its the player not the headphones).
Also there is something shaking around in the player.

Has anyone else had this problem? Can it be easily fixed?
I tried opening it, but after I took out the screws, I didn't know how to actually separate the case.

Its this kind 4GB 2.4 Inch MP3/MP4/Game Player With Camera (HF167)-MP3 and Media Players-