I recently obtained a Dell Inspiron 580s with a ATI Radeon HD 5450 graphics card. This card puts the audio out through the HDMI, I drug my big flat screen from the living room to the office to check this out. My dual monitor setup only has DVI in with an additional audio jack with built in speakers. My onboard audio has probably been disabled when the graphics card driver was loaded. Can I enable my onboard audio to plug in my monitor speakers?
You should be able to connect the speakers to the rear MB ports and choose the on-board sound as the default device in Control Panel/Sound/Playback. If you installed the gfx card driver when connected to a TV with speakers, the TV's speakers were probably switched as the default by the driver.
In my control panel under sound/playback is HD audio control and that is all. So I am assuming that the onboard audio has been disabled when the card was installed. I have no options for speakers at this time. I got this computer with this card already installed. There are surround audio jacks on the back that have no output, additionally the headphone jack has no output.