First of all, have you got the right Realtek program? I'm not completely sure, but i think there are different installers/programs/codecs for it, so make sure you downloaded the right program!
Have you also tried uninstalling the drivers
, restarting and reinstalling? I'll give you a walkthrough (courtesy of fireberd):
Start Menu > Right Click on computer, navigate to and click on Properties > Click on Device Manager (top left) > Navigate to Sound, Video and Game controllers > Right click on the device you are using (In this case, it should be some kind of "High Definition Audio Device") > Right click on it, and click on Uninstall (do not, however tick the box to uninstall drivers) > Restart your PC
I hope this helped, i'm having sound issues too, i know what it feels like!