Pretty simple mark, look at the back of your tower.
From where the monitor cable for the video signal from the tower goes to the monitor.
If you look on the main I/O shield you will see another set of video ports, take the cable from the monitor lead that goes into the computer and connect it to the other video ports on the main I/O.
You will then get a picture on your monitor screen.
Go back into the bios.
And set the Graphics interface mode to Pci-e, or peg mode.
save the new settings before you exit the bios.
Now swap the video lead from the monitor to where it was connected in the first place on the back of the tower or computer case.
The next time you power up the computer an image will be displayed on your monitor screen.