Alliedassault - headphones = the shiter

Well I have had these plantronics headphones for about 3 months and just recently I was only able to hear out of one ear. So, I bought the same pair again. This happend to them too, I can only hear out of one ear. So someone told me it was probally my soundcard. So I bought a new sound blaster live 5.1 and it still does the same thing. Any suggestions? Someone said it is my motherboard, but I have no clue. Could it just be that plantronics and my cpu doesnt get along? Oh and the headphones are Plantronics DSP-400 PC Headset, Cost about 50$ at bestbuy.