no promises but you could try this:
Check you have the right Realtek version. I've encountered problems with that crapo on Asus before and you have to have the right one. Best off using the original driver disk from the board (you have it?) as below:
1) Deinstall Realtek drivers and realtek software
2) after you de-install the drivers go into control panel --> add/remove hardware --> Uninstall/Unplug a device --> Uninstall A device --> Check "Show Hidden Devices" --> See if anything realtek is left on there and if so remove it.
3) Shut down the PC
4) Reboot & check onboard sound enabled in BIOS
5) Re-install ALL the motherboard drivers in their normal order.
If that doesn't work try again and clear the CMOS between shutdown and reboot.
Driverguide.com is excellent for finding drivers. Often easier than the manufacturers site. O/W if you havent got the disk someone on here could send you the iso if they have the same mobo.