|Try the USB headphones in all USB ports built into the laptop, if you haven't already. |
If you still get sound on only one side....
It's likely the USB headphones have a damaged cord. Try them with another computer. If you still get sound from only one side, a broken wire inside the cable is the problem.
The headphones jack on laptops and netbooks has a mechanical switch inside of it. It's supposed to disable the sound from going to the speakers built into the laptop whenever you plug a plug (on a cord) into the headphones jack.
If you have plugged into the headphones jack a lot, it's common for that mechanical switch to malfunction. You could try plugging a plug into the headphones jack, wiggling it, then pulling it out, that may get one or both speakers working, but the only real solution is to replace the headphones jack - that's an item frequently replaced by laptop repair places.