I moved an 2.5” SSD from my old laptop to new NUC, hoping to simply boot up without having to reinstall Windows 10 and other software. I did not install a M.2 drive. When I try to boot up, I get “A bootable device has not be detected.” I have a retail version of Windows 10 activated with my account. The SSD is listed in the SATA Port under the Advanced>Storage screen for the BIOS.
It is very likely that your old Dell is legacy boot. Your new nuc is set for uefi boot, which is why there is no bootable driver found.
I do not have a 10th gen NUC to look in the bios to see if legacy boot is even offered. If it were offered, you could switch from uefi boot to legacy boot. Then, you could convert the drive from MBR2GPT (do a search on this on the web) and convert your drive. Once the drive is converted to GPT, you could reboot to the bios, switch back to UEFI boot, and now you are running a GPT UEFI boot.
I would tell you to do this on the laptop, if it offered UEFI boot in the bios. However, being as old as it is, it probably does not. If it does (and you can determine this by looking in the bios), boot normally, do the MBR2GPT, reboot to the bios, turn on UEFI boot, and boot the drive.
Now, If the laptop does not have UEFI boot, and the NUC does not have legacy boot, you might be able to get away with having the drive on the laptop booted in legacy as it is, do the MBR2GPT, shutdown the laptop, remove the drive and put it in the NUC (that has UEFI boot), and boot the drive. If you were to do this, be patient during the boot process.
All of this said is assuming you have a good backup before you start.
Or, you could simply do a clean install of Windows 10 on the NUC. No key? Not a problem if you have a W7 or W8.x key on the laptop, or even a W10 key.
Report back with your results.
I ran mbr2gpt in validate mode, and got the message that “disk layout validation failed”. This sounds like I’m having to reinstall Windows. To use the Legacy boot mode for the NUC basically requires that action as well. On to Plan B, I guess. Thanks for your help.