Did you install the nVIDIA audio drivers when you did this driver installation? They don't play well with Realtek sometimes. Have a look in "add and remove programs". If you installed the nvidia audio I would:
1. Go download your motherboard realtek audio drivers, DDU, and your GPU driver from nVIDIA
2. Boot into safe mode and have DDU clean out anything that nVIDIA installed.
3. Boot into normal mode, look in add and remove programs and make sure everything nvidia is gone and install your audio (realtek, etc) drivers and verify your sound is working. Try restarting if you can't get sound and look in the sound control panel for sources.
From there I would reinstall the graphics card drivers and only select the display driver and physx, leaving everything else out.