found some one have same problem but without a solution 

https://www.dell.com/community/PowerEdge-HDD-SCSI-RAID/PowerEdge-R420-Boot-mode-only-UEFI-after-installing-NVMe-SSD-via/td-p/7749188

Hi,

I found that you posted before on a separate issue with drive detection. May I know if you already have data in the server? Have you tried clearing BIOS configuration by following the steps here: https://dell.to/3aUk2bw. Try all the steps provided.

Let me know the outcome. 

Hi, 

Do you have iDRAC access? Would you be able to check if the BIOS version has rollback option following this steps: https://dell.to/2L3c58Q

What is the current BIOS version? 

no I don't have any data only windows server 2019 
yes I tried all the steps in the link 

bios version 2.9.0

Hi,

Have you checked in iDRAC if BIOS rollback to previous version is possible? If not, can you try downgrading the BIOS version to 2.7.0.

Let me know if the issue persist after downgraded to version 2.7.0.

let me tell you how the problem exactly happened....in normal Scenario when the server start black screen start with memory config - done than IDRAC initialize after that the server start
but in the server i have the memory config and IDRAC initialize start twice

its not possible to rollback ...tried version 2.7.0 and still same problem
and the hardware test didn't found any problem 
btw after bios return to default i got this message:  

Invalid configuration information

ok ok ok i got news If I do not unplug the power cord, the device is working properly.....But when i disconnect the power cord the problem occurs....i tried to change the battery but still same problem

ok it's look the problem from battery base

the pictures 

https://ibb.co/3NsWVkG
https://ibb.co/jL7NtVW

Hi,

the Mainboard needs to replaced probably.

regards Martin