Need more info for better troubleshooting.
Does it not "post" or does it not "power on", no post means there are LEDs on the motherboard being lit up but does not result in video out to BIOS screen. "NO POWER ON" means NO LEDs on the motherboard light up.
If no power on, then recheck PSU (power supply unit) & Casing connections (on/off, reset wires etc), or change PSU. Use the "Q-Code Power Switch", which is on the motherboard to turn on. Follow this guide for No Power
https://rog.asus.com/support/FAQ/1042632
If it powers on but gives beep then check for number of beeps, Asus ROG x299 has a Q-Code LED that displays the error code, follow the error code if it shows any. Follow this guide for Q-Code troubleshooting
https://rog.asus.com/support/FAQ/1042678
Codes =
https://rog.asus.com/support/FAQ/1043948
I would just do basic troubleshooting to see if it is really a hardware fault that needs repair or just a configuration/connection mistake, hope it helps, best of luck