Check for silly errors like the monitor is switched to a different input. Try a different output on your current card. HDMI or VGA instead of DVI. No offence, but even us old farts make some stupid mistakes once in a while. Then you have to try a different graphics card. Does your Asus MB have the four indicator lights to show if the CPU, RAM, GPU and HD are all reading at boot. IF any of them stay on then it means that device is not working.