Not always, but sometimes i use my radio as spakers with my PC (great bass

Before, i used the USB connection, and everything oworked just fine, but i had my radio on the floor, which resulted in me driving my chair into the plug, making the USB connection to the radio unusable..
So now i use the gameport (red and whit plug, you know). But i only have sound in my right speaker, anyone knowing why this happens?
The radio is a Philips az2558
Runar