Uninstall your present drivers
. Then reboot, let windows detect the sound card and install whatever driver
it wants to install. Then try these one by one.
1) Install your realtek drivers manually from the device manager by right clicking on the sound card and selecting Update driver, then point it to the location of your realtek drivers. Make sure you have the correct drivers.
2) If 1) does not work, again go to device manager and update driver but this time, let windows go online and update the driver by itself.
If nothing works, try using the Vista driver for your card.