Start your computer in safe mode (Start machine, poke the F8 key once per second until a B+W screen shows up with multiple items to choose from. Use your cursor key to move highlight to the top, "Start in Safe Mode").
Just when you think Windows is going to show up, a question is presented, asking you if you want to perform a system restore point rollback, or to continue into safe mode. Make choice to continue into safe mode.
Right-click the desktop in a vacant area.
Move mouse to select Properties and click
Click the Settings tab
Click the Advanced button
Click the Monitor tab
A small box labeled "Screen refresh rate" is in the middle of the box, Click the little down-arrow on the right side of the box.
Select 60 Hertz.
If the screen goes dark and stays dark, don't touch anything, it will return in 15 seconds. Try a different one, or come back and say what your monitor is, brand & model. If it is a LCD monitor, don't bother trying the 30 Hertz or lower.