Most Crt have a higher refresh rate, Around 75-85hrz range. This is because a CRT renders the screen by sending bursts of electrons down a vaccum tube which are deflected by magnetic fields to strike the phosphor layer on the screen itself. How many times it does this is representative of the refresh rate. CRT's have been known to flicker at less than than ideal r-rates, consequently you may experience this at such a low rate. Check the Nvidia control panel. If you haven't already, install latest video drivers, and if applicable monitor/display drivers. If the monitor has a strict 60hertz refresh rate, you can't change it.
LCD monitors don't physically need refresh rates, because they use vastly different technology than CRT's, no electron guns or phosphorous layers. They are still used however, in part because todays tech is still built around a refresh rate, for example, the video cards frame buffers. [/banter end]