1. Check if the audio jack is securely connected to the sound card.
2. Test if the headphone is working by plugging it to another device.
3. Check the audio settings on your computer. Make sure all the channels are working at maximum volume. Ensure the audio output is set to the headphone jack.
4. Check the default audio device for your computer. If it is set to the wrong device, you will need to change it to the correct one.
5. Ensure all the drivers for the sound card are updated to the latest versions.
6. Check the sound card itself. If it appears to be faulty, replace it with a new one.
7. Look for any loose connections inside the headphone jack. If any of the wires are loose, carefully tighten them.
8. Try an audio port testing tool to check if any of the pins are damaged.
9. Run a scan for any malware infections that might be blocking the audio device.