Recently, one of my colleagues snapped his earphones in the front Audio Jack of his machine. So he tried using the Rear ones with a different headphone. But the audio wasn’t coming. So I did a bit of troubleshooting and found that, since the old earphones snapped, it left a small piece of metal in the front audio jack. So the machine thinks that the audio jack is in use and it takes over the rear jack from emitting sound.
The only way to disable the front Audio jack is to physically disconnect it. There is no BIOS or software setting to disable it.
If your machine is an old one, there might be a chance that the front Audio Jack is connected individually with a cable to the motherboard. Open the case and locate the cable and disconnect it. The front Audio jacks are simply an extension to the original back ones, but they detect the earphones and take over the rear jack.
All the latest DELL machines have the power switch, front USB ports and Audio jacks on the same circuit board connected to the mother board with a single connector. If you disconnect that, you won’t be able to switch on the machine. So that’s not an option with the new machines.
Remove the circuit board and break the Audio Jack. That’s how I fixed it :)
Note: You can always the disable any (front or rear) of the USB ports from the BIOS, but not the Audio Jack. You can completely disable the onboard Audio controller from the BIOS.