Use VGA Mode to Troubleshoot Monitor Refresh Rate Problems
Have you ever accidentally set Window's resolution or refresh rate to a level that was not supported by your monitor, only to find that you could not change it back since the screen had become an unreadable mess? This annoyance remains one of Window's biggest hidden booby traps, especially for users with older monitor hardware.
Setting the refresh rate or resolution higher than your monitor can display will result in a garbled or blank screen, and a huge headache if you accidentally keep the settings. Fortunately Windows XP includes an easy way to reverse monitor resolution problems in the form of 'VGA mode.'
The VGA mode option on the Windows advanced options screen (accessed by pressing F8 repeatedly as your computer is just starting up) will start Windows normally but with a basic VGA video driver at 640x480 resolution and 60Hz refresh rate. Any VGA monitor can handle this, so you will be free to go back into display settings and change them to something your monitor can display properly.
To recap, if you can't see the screen in Windows XP due to refresh rate settings, reboot your system, pressing 'F8' repeatedly as the computer restarts. From the boot menu, choose 'enable VGA mode'. Once Windows starts up, go to the display settings and try a different resolution and refresh rate setting.