On a machine that is a due for replacement (Dell Dimension 4100) running XP and now failing to boot up, I need to find the problem. The power-up sounds normal with fans running, etc. but the only display is "check monitor cable". I installed a graphics card and plugged the monitor into the new card but still get same message. What else can I do to determine if the motherboard is shot or if it is another graphic/video issue? When the computer is plugged in there is a green light on the MB. Any suggestions are appreciated.