I cannot seem to get 120hz refresh rate on my Asus G55V laptop. The specs indicate it to be possible on this unit but... Device Manager only lists PNP Generic Monitor and I cannot update or find a specific driver.
They shipped that model with 3 different display options. What is your screens max resolution? The 3d screen uses a 720p res, so if you are using 1080p then you don't have the 120HZ option. Tye driver for the 120hz display is on Asus's website in the driver section for that model listed under Other-> naked 3d panel https://www.asus.com/Notebooks_Ultrabooks/G55VW/#support