I have recently built my first pc but sadly no sound plays, but don't think i am an idiot because i have check the volume, the device, the jack, the drivers, and i have replaced the sound card, soon i will be updating my CPU but, the only thing that i have not done is reinstall windows 7 which i will try soon (as i am not at home) but if you have any other ideas, they would be very useful!!!
I would check all sound settings in windows, I know my asus d2x can be a bit iffy with drivers, so my other call would be uninstall drivers, reseat card and then reinstall.
Have a look in Device Manager and see if there are any warning signs next to your audio device and see if you can fix it from there.