Recommend trying the simple stuff first. Check that the GPU has power connectors connected to the top of the board and that these connections are secure and latched into place.
Make sure that the monitor works, then connect it to an output on your GPU and try a system boot. Some monitors do not auto-detect the GPU output so you may have to do this manually.
If there is a video failure, you should hear a beep code and (with luck) your MB will have a digital display that shows an error message. With luck, this will be an easy fix.