I spent several hours searching the internet for a solution to this problem and here is what worked for me:
My issue: No sound when playing videos in Internet Explorer 7 using Windows XP SP3 with the ASUS P5N-E SLI 650i motherboard using the onboard sound (Realtek). I was able to hear sound playing MP3s using Winamp and videos in the VLC media player. However, this fix might also work for other types of sound issues with XP SP3 and this motherboard.
As of this writing (November 2008), Microsoft Windows XP Service Pack 3 (SP3) does not support the Universal Audio Architecture (UAA) driver for High Definition Audio devices, which is required for the sound to work properly. Try this to fix the problem:
1) In Control Panel / System / Hardware tab / Device Manager under Sound, Video & Game controllers, disable then uninstall the Realtek High Definition Audio device (and/or the unknown device, if there is one).
2) In Device Manager under System, disable then uninstall the Microsoft UAA Bus Driver for High Definition Audio entry. (Do not re-boot yet.)
3) In Control Panel / Add/Remove Programs, uninstall the Realtek High Definition Audio Driver (you may just have a folder that says Realtek).
4) Reboot the PC.
5) Install the Realtek audio drivers then reboot again.
6) Download a patched version of the Microsoft UAA for SP3 here:
Download the file from this link:
Fix for KB888111 for Windows XP SP3 RC v3264 (Mirror)
--> filename: Universal_Audio_Architecture_High_Definition_Audio_AddOn_1.0.zip
--> unzip to folder: Universal_Audio_Architecture_High_Definition_Audio_AddOn_1.0
Navigate to that folder and run hdashcut.exe - it may appear to do nothing but wait for a minute and then check Control Panel / System / Hardware tab / Device Manager under System. If you see "Microsoft UAA Bus Driver for High Definition Audio" listed there, it worked. Reboot the PC again.
ALTERNATE SOLUTION TO REPLACE STEP 6 ABOVE:
1) Download the Microsoft UAA patch for Windows XP SP2 : http://support.microsoft.com/kb/888111
2) Start menu / Run... / regedit (opens the registry editor) and navigate to :
3) On the right side of the window, double-click on CSDVersion.
4) Change the value data from 300 to 200 (this makes XP think it is running SP2 instead of SP3). Close the registry editor then reboot the PC.
5) Install the Microsoft UAA Patch you downloaded in step 1.
6) Repeat steps 2 and 3 to access the registry editor, then change the CSDVersion value data from 200 back to 300.
7) Close the registry editor then reboot the PC.