Uninstall and reinstall the drivers.

Also verify if you have a motherboard VGA port that you have the monitor plugged into the graphics card and not the motherboard.

.. when i booted my computer in safe mode and i clicked propeties settings & advanced and then i clicked on the monitor tab but it wouldnt let me change the refresh rate when i try to change it, it says "use hardware default settings"...

Uninstall and reinstall the drivers for your graphics card.