Here`s what the problem is.
The board has its own video output.
That is set as the default primary display adapter for output to the monitor.
If you connect the monitor to the back of the video ports of the board.
You will get a screen image.
You must next enter the bios and set the primary display adapter as the Pci-e interface.
Save the setting in the bios before exiting.
And then connect the cable from the monitor to the back of the 780 card.
you will then get a display image from the 780.
Msi boards are notorious, for not auto switching on a pci card fitted in the slot, you must manually set the interface to pci-e in the bios and save it then it works with your 780.