Thank you.
Yes, to look at the PSU you have to go into the tower, but I think we can skip that for right now.
According to ASUS the sound chip on your motherboard is an "ADI AD1986A SondMAX 6 channel CODEC."
This part doesn't show up on your 'sound' screen shot. Two things possible:
1st. The part has died, the sound chipset is no longer functional. Very probable. This is an extremely old system (7 years or more) and may have finally worn out.
2nd, and this is a little better, the driver for the sound may have become corrupted. Below if the link to ASUS:
http://support.asus.com/download.aspx?SLanguage=en&p=1&m=P5VD2-VM&hashedid=2sYAtam7ng8vCngf
You will have to select an operating system, then download the newest audio drivers and install them. NOTE; ASUS ONLY
SHOWS SUPPORT FOR THIS BOARD THROUGH THE Vista OS. If you are running Windows 7, try the Vista drivers.
If you try to install the drivers and get a notice to the effect that the sound device cannot be found or is not installed, that is going to tell you the sound chip/'card' is dead.
If the chip is dead you could buy a PCI Sound card and install it in one of the long white PCI slots, but personally I wouldn't spend anymore money on this pc if I could avoid it. Best Buy has a Creative SoundBlaster Audigy SE card for $29.99 and they used to have a house brand (RocketFish) for that much or a little LESS that had the Creative chip on it.
Jumping ahead of myself, before you install ANY drivers or new hardware, go into Control Panel, Programs and Features of if you are using XP 'Add/Remove' programs and uninstall the Avnex audio device.
AMD High def. is on the video card and is meant ONLY for HDMI output to a T.V. or audio receiver; if your monitor has speakers AND an HDMI connector, you could disconnect your DVI or VGA cable connect the Video card to the monitor with an HDMI cable and you would have your sound back.