Easiest way to fix this is to just use your onboard video card. Look in your computer case and you will see a DVI or HDMI connector that is located on the motherboard, not on the GPU. Plug your monitor in there.

If you start your computer and got a blank screen, you need to enable it in bios first. So plug back into GPU the monitor, go into bios and enable onboard video. Then you should get a display.

Now you can mine at the same time without slowing down your computer or mining speed. Only issue you might encounter is the GPU might not work unless a monitor is plugged in. If that is the case then you need a HDMI dummy plug.