Have you tried using ONLY an HDMI cable to the graphics card? No Displayport or DVI.
Try other outputs than whatever you've tried so far on the graphics card outputs, and see if you have any luck. Also, I would check to see if there are any BIOS updates for your motherboard, and if there are, I would update using the RX 470 and then after updating, try again with the 5700xt. Also, it couldn't hurt to try a hard reset of the bios WITH the 5700xt installed.
BIOS Hard Reset procedure
Power off the unit, switch the PSU off and unplug the PSU cord from either the wall or the power supply.
Remove the motherboard CMOS battery for five minutes. In some cases it may be necessary to remove the graphics card to access the CMOS battery.
During that five minutes, press the power button on the case for 30 seconds. After the five minutes is up, reinstall the CMOS battery making sure to insert it with the correct side up just as it came out.
If you had to remove the graphics card you can now reinstall it, but remember to reconnect your power cables if there were any attached to it as well as your display cable.
Now, plug the power supply cable back in, switch the PSU back on and power up the system. It should display the POST screen and the options to enter CMOS/BIOS setup. Enter the bios setup program and reconfigure the boot settings for either the Windows boot manager or for legacy systems, the drive your OS is installed on if necessary.
Save settings and exit. If the system will POST and boot then you can move forward from there including going back into the bios and configuring any other custom settings you may need to configure such as Memory XMP profile settings, custom fan profile settings or other specific settings you may have previously had configured that were wiped out by resetting the CMOS.
In some cases it may be necessary when you go into the BIOS after a reset, to load the Optimal default or Default values and then save settings, to actually get the hardware tables to reset in the boot manager.
It is probably also worth mentioning that for anything that might require an attempt to DO a hard reset in the first place, it is a GOOD IDEA to try a different type of display as many systems will not work properly for some reason with displayport configurations. It is worth trying HDMI if you are having no display or lack of visual ability to enter the BIOS, or no signal messages.