Is there no video only on the external display, or on both the laptop and the external monitor? If only on the externam monitor, your resolution and/or refresh rate is probably too high. Use both screens, and set the resolution on the second display. For a 17" LCD, you probably will be using 1280x1024 at 60hz. If you had a CRT before you may have had it at some odd refresh rate that the LCD can't display.