Ok. So i searched up this same question on this same site but i have not found the solution yet. I just bought some new gaming headphones and when i plugged them in, only the left side worked but the right side didnt. I also plugged in other headphones and the right side doesnt work but the left does. My next step was to connect both my new gaming headphones and the other headphones in my mp3 player. It worked perfectly. Now i know it isnt the headphones. What now? P.S. I use really old headphones from like the 90's so i have to use a adapter to be able to hear it on the pc. (the original jack is too big.) ( I also have speakers, the speakers work fine.)