I have tried every command known to man. I've tried adjusting alsamixer, pulseaudio, and the master volume. I have no idea what to do. I restarted my computer after a friend of mine had fixed it, and now it's back to what it was doing before. Could someone explain to me in a step by step fashion how to disable the stereo so that I can listen to music just through my headphones, not both?

How are the headphones connected? Is it a headphone jack on the machine itself, or is it connecting via USB?
If it is connecting via a headphone jack, then this may be caused by ALSA not detecting the presence of the headphones..