Question : Problem: NO onboard audio for ADI SoundMAX 6-channel Audio CODEC for the Asus A7V400-MX Mobo.

Clean install with XP pro. Used MB install CD, downloaded latest driver from Asus website. Enabled in BIOS. Used different speakers, volumn turned up. CPU is an Athlon XP 2600 and 1 GB Ram.

Answer : Problem: NO onboard audio for ADI SoundMAX 6-channel Audio CODEC for the Asus A7V400-MX Mobo.

Try to update the BIOS, also try resetting BIOS to default settings.
If it didn't help then it might be motherboard defect.