Try and see if your monitor works on different computer to verify the monitor is working correctly. You should also check to see if you have any loose connections inside the computer, remember if the cable doesn't look like it goes anywhere it's probably just an extra cable.
well there could be many things wrong with the system itself but first off i would try testing the power supply on the machine and if that works fine i would test the motherboard to make sure it is getting full power and the easy of them all is that the swith is going out on the system case
If no lights come on at all, the power supply is burned out. If you get lights on, it may just be a loose cable inside. Get a friend who is knowledgeable about computers to open it up for you.
