First off, please include/list your specs like so:
CPU:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
OS:
For the sake of reference, please state which version of BIOS you're currently on. If you're working with one stock of ram, then DDR4_1 is the only slot that you need populating. If you're on a dual channel ram kit, pass on a link to said kit and then see if you can reflash the BIOS for the motherbaord with one stick of ram.
Once (re)flashed, power down the system, drop both sticks of ram in and then with the system disconnected from the wall, remove the CMOS battery for at least 15 minutes.