Is the disk is detected by the RAID controller you have on the server? You can check this in Controller BIOS and iDRAC. Is the new drives are procured from Dell? Can you also check the LED status for these drives. You can refer below link on LED status code [URL] 
Hi, I have a Power Edge R440 Server with windows server 2019 Installed. Now i am trying to add more HDD (Exos 10E2400) on the server but it is now detecting the HDD.
Hard Disk not detected on poweredge R440