no signal from computer to moniter

Their is no signal from my Asus essentio to the monitor . The monitor is working fine as I have cctv cameras attach to monitor and it is displaying them fine, I have also checked cables which are all fine. This has lead me to believe that this could be the graphics card . I have taken a look inside the computer and I can t see the normal set up with a removable graphics card attached to the vga port so I am now wondering if the whole motherboard needs replacing. Thanks