I been trying to overclock my Graphic card through RivaTuner but it wont let me, every time I increase the core clock and memory clock and click on apply they go back to default, I also tried Ntune, it wont let me even drag the arrow thingies to the right, its just stuck there.
Depending on the brand some lock there cards bios to not allow overclocking. Try useing EVGA precision i like it better then rivatuner and its easier to use. Also make sure u have the newest drivers and the newest version of rivatuner.