PC Assembled, but no display

Troubleshooting new PC builds are and do deserve an entire book's worth of possibilities. Boiled down to the basics you are looking at a process of elimination to slowly verify and weed out each component that works until you find the one that isn't. I highly recommend looking through the many ifixit troubleshooting guides or simply googling one (youtube is silly with them if you hate reading).

The main information that will help you troubleshoot a preboot or prePOST issue is the onboard indicator on the motherboard. In your case this is likely just a buzzer/beeper that will emit coded tones to indicate which part of the boot up process has been reached or failed. Here is a link to the Asus default guide on this but you could/should also look up the specific ones for your motherboard and where/what the indicator is.

https://www.asus.com/us/support/FAQ/1029...

That being said if everything is working correctly and POSTing you could try using the alternate graphics outputs (HDMI instead of DP vis versa etc) in case the default output pre-driver install is not the one you have plugged in.