There can be two reasons why it isn't working of the front connections...
1. The front panel audio connectors aren't hooked up to the motherboard
2. The software is set up so that if any type of speaker is connected in the back, nothing else that can output audio would work.
If turning off the speaker gets sound coming out of the heasdet then 2 was your problem, but if even disconnecting the speakers from the back doesn't result in sound from the headset then you'll have to crack open the system to see if the front panel audio header is actually connected to the motherboard.