If you've just built a new PC and it's not displaying anything, there are a few things that could be causing the issue. Let's go through them one by one.
First, check all of the cables to make sure they're properly plugged in. This includes the power supply, graphics card, and any other relevant cables. If everything is plugged in correctly, your next step is to check the BIOS settings. Make sure that the correct display output is selected and that any integrated graphics are disabled.
If your BIOS settings are correct but your PC still isn't displaying anything, it's likely that there's an issue with your graphics card. Try removing and reinstalling the card to see if that fixes the problem. If not, you may need to get a replacement card from your retailer or manufacturer.
Hopefully this troubleshooting guide has helped you get to the bottom of why your new PC build isn't displaying anything.