G'day darryl,
click on your start button at the bottom left on the screen and select
control panel. this will bring up a window which will contain several
categories, from this choose "appearance and themes".  here you will find a
section which says " pick a control panel icon", click on "display". this
will bring up another window which has 5 tabs choose the one marked
"settings" and click on the advanced button which appears. another window
will appear which has 6 tabs, click on "monitor". in the monitor section
there are 2 boxes. in the lower one marked "monitor settings" there is a
drop down menu which gives you the choice of three refresh rates ( at least
that's how many mine has), highlight which setting you want ( i have mine on
75 hertz) and leave the tick in the box. then just hit the ok button and
close the control panel, and that should take care of it. good luck!
pablo