How do I get my PC to display without a GPU?

You'll need a GPU if your CPU doesn't have integrated graphics. Without a dedicated GPU, there's no way to get a video signal.

Check the lights on your motherboard, especially near the red light. If it says 'CPU' or 'RAM', there might be a problem with either the CPU or RAM seating. Make sure everything is connected properly.

Could you share your full specs? It’ll help in figuring out what might be wrong. What CPU and motherboard are you using?

To get a display, you have to connect the monitor to the motherboard directly. But make sure your CPU has integrated graphics; if not, you won't get any video output just like you’re seeing now.