garbled display when changing refresh rate

[drewdude420]

I just built my new computer today and put in a Radeon x700 pro. All is well until I want to change the refresh rate of the monitor to 75hz from 60. Sometimes, but not always, the monitor will display just weird garbled lines of color and my computer will be rendered useless until I restart in safe mode. Even if it doesn't do this right away after I change the setting, on the next reboot it will do it. Is my video card broken? Help!!! 60 hz gives me headaches .

Also, which is the better card: Geforce 6600 LE 128mb or Radeon x700 pro 256mb?

Thank you!!