Well if its nothing on the software end, then it would either be a bad motherboard or front audio panel. If sound still works through the back (which it would seem that way) I wouldn't think it would be a bad audio chip on the motherboard, but possibly a bad header (I feel like that would be unlikely, but possible).
You could always get into contact with your case manufacturer and see if they will ship you a new front I/O panel. NZXT did that for my case when one of the USB 3.0 ports died. It took a few weeks for everything to get shipped and get here but it was completely free. I didn't even need to send back the old panel.
You could also invest in a cheap discrete sound card that has front panel capabilities like the Xonar DGX. I personally use this card and have no major complaints.