Motherboard replacement Optiplex 9020 with Windows 10

The power switch was flashing a - 2 and then 1 sequence on this PC, which according to Dell troubleshooting is a bad motherboard.  I replaced the motherboard with a refurbished board of the correct model.  When I booted up the system, the screen flashed a message that the system was in manufacturing mode and to go into bios to reset it.  I tried this using ALT-F, which appeared to reset the bios to default, but upon rebooting, the same message flashed on the screen.  To make the problem worse, windows did not load and a message came on the screen saying no boot device was found.  I rebooted and this time hit f-12 for the boot menu, which showed the hard drive in the list.  I selected the drive and the system booted into windows.  I noticed that windows was showing that it was not activated.  I assumed that this is a glitch with the upgraded windows 10.  I'm thinking that he old board has the activated windows key in bios, but the new board does not. So I used the windows 7 key on the sticker and activated windows and this succeeded.  However, upon rebooting I still receive manufacturing mode and the no boot device found message, but using f-12 I can still get windows to load.  I went into bios and tried several things, like making sure the hard drive was first in the boot list, etc.  Bios is set for legacy mode.  I tried to change it to uefi, but this did not work.  When I tried to add devices, the uefi setup said it couldn't find the device list.  I also tried recreating the boot track from recovery mode, but this also did not solve the boot issue.  I am planning to try going back to the original motherboard to see if it can boot correctly, but I'm concerned that I may still have boot problems.  My questions are:

- Why can't I get the board out of manufacturing mode?

- Is there a way to get the system to boot up correctly or will I have to reload windows from scratch?

- Is there a chance that the original motherboard will work correctly?  Ironically I have found out that the motherboard is good and the original error condition was caused by the add-in video card, not the motherboard.

I really need to avoid a windows reload and appreciate any suggestions.