Many modern computers do not have standalone sound cards. Instead, the motherboards in these computers have integrated chips that produce audio. Because these chips cannot be removed, it isn't technically possible to replace the sound card in such a computer. However, you can still install a sound card or external audio device. After doing this, you can disable the integrated audio chip from the Windows Device Manager or motherboard settings.
kevin make sure in the bios your audio chipset is turned on. also look in windows audio control panel. make sure your sound not muted and make sure windows is using the realtec hd device and not ati or nvidia hd output. if it is then your computer going to be trying to send the audio out the hdmi port.
if you have the windows speaker icon in the lower right of your screen click on it and open volume control options. the audio output device will be there. make sure default button is clicked and reteck devices are clicked.