Right-click your desktop, then select Properties. Click the Settings tab. On that tab, click the Advanced button. On the new popup menu, click the Monitor tab. On that tab, click the Refresh Rate menu, and then select the highest number you see, which should be 85 Hertz.
The human eye can perceive 60 Hertz, which means that whether you actually see it or not, that flicker is penetrating to your brain. Causes headaches. This will help.