Do the fans spin up when you hit the power button?

You could make sure everything is seated properly. Push on the two large video cards into the riser slots underneath them.

Or if your motherboard has an HDMI or Display port or some video output, you could disconnect the two large video cards mentioned above and see if that helps. Maybe one or more of them are bad.

Make sure l power cables are plugged in everywhere.

Make sure the RAM is seated properly. The red little board in the yellow slot.