I guess your video card puts out a resolution and/or refresh rate too big for your monitor. You should start your windows in VGA mode (at startup hit F8 key and then choose VGA mode) and then change resolution and refresh rate to something that suits your needs. If you change to something unsupported by your monitor again just hit the N key or restart in VGA mode and try again. You could maybe install a driver for your monitor (if you have it) so windows would detect the monitor correctly.