I installed an HD 4670 AGP into a Dell Optiplex GX270. The sound works from the speakers which are plugged into the back of the computer. I like to use headphones using the front headphone jack.
When i do this sound comes out of the left headphone speaker and the right computer speaker. So the computer is recognizing the headphones but is splitting the audio between the two.
When i installed the card a new device was installed ATI High Definition Audio Device. I have disabled it and the problem still persists. I have uninstalled it but when i restart the computer it is back.
The ati HD audio device is for HDMI output on card.
Something tells me something is wrong with the headphones.
Did you try a different pair and are you sure they are fully plugged in.
Also try wiggling the wire near the hdphone plug and also slowly
pull it halfway out.
If doing this you get full sound from phones then it is a bad plug.
Very common for a bad plug on headphones.
also when you installed video card maybe you partially pulled out front panel