Monitor has no display

I have a friend's Gateway Model#GT4015E computer. It has onboard video but it now does not have any display at all! I have tried it on one of my regular CRT's and it reads "out of scan range." On my LCD it shows "no signal". The computer appears to be passing POST and there appears to be cpu and hard drive activity based on the HD LED activity light and the computer sounds as if it is booting up fine...there is just no display...ever!! I have tried installing a known good pci-e video card but the monitor acts as if there is no display at all....like there is no signal. I think this may be because the motherboard isn't configured to send video to the secondary video card but I do not know how to disable the onboard video as I do not see any jumpers that indicate this function. I have tried pressing f8 to see if it would bring up the safe mode prompt but again...nothing! I know a decent bit about computers but this one has me stumped...please help anyone!!! By the way the MB is a C51GU01.

 

Take out the extra video card and hook up the CRT. Don't press F8, keep tapping it while the computer boots up. If you see "out of scan range" at least something is displaying on the CRT. Then select safe mode. Right click the desktop, properties, settings, advanced and change it (make sure that Hide modes that this monitor can not display is checked/ticked).

 

When I said that I pressed f8, i meant that i repetitively tapped it....but there is no display at all. Just a very brief (less than 1 sec) message: "out of scan range." There is no hope of doing anything inside windows because you cannot ever see anything.