change frequency of your monitor in XFree86: More colors makes your video card transfer more data during the same time. If your video card cannot cope, then either the resolution has or the refresh rate has to be reduced. By default, XFree reduces the resolution. If you want to keep the resolution and reduce the refresh rate, you must insert a new appropriate Modeline into your XF86Config file which defines that resolution with a lower refresh rate. For instance replace the old value # 1600x1200 @ 70 Hz, 87.50 kHz hsync # Modeline "1600x1200" 189 1600 1664 1856 2160 1200 1201 1204 1250 -HSync - VSync Modeline "1600x1200" 185 1600 1664 1856 2160 1200 1201 1204 1250 -HSync -VS ync The magic number 189 and 185 are the respective clock rates which you find reported by X in your .X.err file. Then start X server: % startx -- -bpp 32 >& log |