Check in this forum for your other post reply.

You did not mention it but did you install Windows on the drive ? If the answer is yes, does the BIOS have AHCI enabled and UEFI and also is Windows Boot Manager the first option in the boot menu?

Hi everyone, I recently bought this Optiplex 9020 MT and upon turning it on I am met with a screen telling me no boot device has been found. In diagnostics it says no problems found however it also says no Hard drive found. I have a ssd plugged in with the correct wires. Any help? Thanks

If the operating system is installed with UEFI before boot sequence is changed, the system can be recovered by changing Boot sequence back to UEFI.

If the operating system is installed with Legacy mode, the system cannot be recovered by changing the Boot sequence back to UEFI mode. 
Operating system reinstallation should be performed.

Follow the steps below to reinstall Windows 10 or higher:

1. From a power off state, power on the system and Press F2 at the Dell logo to boot into the BIOS setup menu.
2. Choose Boot sequence and change the option from Legacy to UEFI then click Apply in the lower right corner of the screen (Figure 2):
    

    

   
   Figure 2: Change Boot List Option from Legacy to UEFI in BIOS settings.

3. Choose Advanced Boot Options and disable Enable Legacy Option ROMs then click Apply in the lower right corner of the screen (Figure 3):
    

    

   
   Figure 3: Enable Legacy Option ROMs in BIOS settings.

4. Choose Secure Boot -> Secure Boot Enable and change the option from Disabled to Enabled. 
5. Then click Apply in the lower right corner of the screen (Figure 4):
    

    

   
   Figure 4: Enable the Secure Boot Enable setting in BIOS.

6. Click Exit in the lower right corner of the screen and wait for the system to reboot.
7. Reinstall the Windows 10 operating system.