I installed a Radeon 6850 into an HP Compaq dc5800 Microtower and the sound stopped working. The Windows Audio service was running and set to Automatic, but the Windows Audio Endpoint Builder service had disappeared. I tried fiddling with the Device Manager and various troubleshooting steps to no avail, so I went to HP's support FTP site and obtained the latest sound drivers for my model.
I wasn't able to reinstall the SoundMax audio drivers (also by ATI, ironically) that I downloaded from the HP support site until I pulled the graphics card back out (sound was back, old lower-quality graphics), and the SoundMax driver can't start if I put the card back in (great new graphics, no sound).
Has anyone else encountered and solved this problem? Please advise and recommend solutions if so.
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Excellent tip to look in the BIOS, thanks; wish I'd thought of that sooner. I ended up not disabling the onboard sound, because I first tried a setting I found labelled "Integrated Audio" in the motherboard list. It was Disabled initially, so I set it to Enabled (figured I could try other things later anyway), and that worked! I now have sound *and* graphics, barring any reemergence of the problem in the future.