First of all, you need to ensure you are using a Dual-link DVI cable and that you have it connected to the DVI-D port on your graphics card. Once you have done that, verify you have the most current Catalyst drivers installed. Restart your PC if you had to install new Catalyst drivers. Once you are in windows, you should now be able to select from an option allowing for 120Hz. You might be able to use the Displayport on the monitor and card as well, but attempt to use the Dual-link DVI solution first.