1. Confirm that the memory is fully installed as shown
2. Check if there is any dirt on the memory Pin or memory slot of Motherboard
3. Please replace your DRAM with the one on Memory support list(QVL list)
4. Please refer to the suggested memory configurations found in the user manual of your model as shown in the below picture, then try again.
You can refer to download user manual
5. If you're using two or more memory, try to boot with only one memory installed, then reboot each time with an additional memory installed.
6.If your problem cannot be solved after following steps 1-5, please change the memory and try again
7. If above setups still cannot solve your problem, please reinstall CPU or change another CPU