You can check this points:
- Windows problem: Some users have reported that you must really "shutdown" pc from Windows8 , just "reboot" cause audio problems. Also, "fastboot" must be disabled in the bios.
Pulseaudio problem: in the "sound parameters" output tab, you should see device automatically changing from speaker to headphone when you plug a jack . As Pulseaudio stores independent level for each state, it could be bad just for headphone .
You can also run this command a terminal to reset pulseaudio config:
rm -r ~/.config/pulse; pulseaudio -k
Alsa setting problem: Do you see "headphones" fader when you launch
alsamixer in a terminal (eventually press F6 function key to select your main soundcard which is the "not hdmi" one).
The fader must be unmuted (check toggle mute by pressing "m" key when the headphone fader is selected via left/right arrow keys). Set fader level with up/down keys.
Finally, a software update solved the problem
If nothing works, run "Alsa-info" to show your audio config (someone can have an idea) : copy the following command in a terminal , choose "upload" option when asked ("tab" key to select it) an post url printed at the end.
wget http://www.alsa-project.org/alsa-info.sh -O alsa-info.sh && bash alsa-info.sh