In order to access the NVIDIA Control Panel in any operating system, the official NVIDIA drivers for your graphics card must be installed. You can
download the drivers for your card from NVIDIA directly at this link. If this is a fresh install, this should work without any issues. If you preformed an update from Windows 7 to Windows 8 and had NVIDIA drivers installed in the Windows 7 environment, you may need to uninstall the NVIDIA software from the Programs item inside the Control Panel to avoid the preexisting configuration conflicting with the new install, a handful of users on various forums have reported such preexisting installs to have conflicted when updating their drivers.