If none of the following works, plug your headphones into the back panel where your speakers are plugged in. That will keep Crysis quiet. Anyhow:
1) Did you plug the Front Panel Audio connector onto the motherboard correctly?
2) Do you have the Realtek HD Audio Manager (drivers, etc) installed properly?
3) Is the Realtek icon in your system tray?
4) In HD Audio Manager, "Speaker" tab, click "Device advanced settings". Check "Mute the rear . . .", and uncheck "Make front and rear . . ."
5) Once that's done, does the audio manager recognize when you plug in the headphones in the front jack? It should ask you to verify you have just plugged headphones into the front panel jack.
If all else is done, and it doesn't recognize you plugged in your headphones, you likely have a bad front panel speaker jack.