Headset Stopped Working...?

Today my headset started acting funny. Basically whenever I watch videos, listen to music, talk to people through skype, etc... I can only hear the background sounds, but not the voices. Does anyone know the cause of this? I've checked to see if my audio card was just going bad... but I don't have this problem with the computer speakers or any earphones, etc. It's not a BIG deal cause it was just a cheapo Logitech Premium Stereo Headset from Wal-Mart lol... I'm just curious as to what causes this so I can avoid it in the future. Thank you! (: