Yet another startup issue after OS migration

Like a number of people, I used the Samsung data migration tool to transfer my Win7 operating system from one SSD to a larger one, and afterwords discovered that Windows would not start unless both drives were plugged in. I have spent the better part of 6 days trying every "Try this and see if it works!" solution I can find on the net, and none of them have worked for me. The original drive is an 840 EVO, the new one a 512 GB Samsung 951 NVME.
A boot with only the 951 connected fails with a winload.exe missing error, and then booting from the install CD into Windows "Repair my Computer" results in the notice that Windows can't automatically fix the issue, and manual Startup Repair produces a no hard drive found message. From the command prompt, only the "Data" partition is recognized on the drive by Diskpart, which makes me think that the partition table on drive C may an issue.
When booting with both drives attached, the Starting Windows screen appears for about 90 seconds before the log on screen comes up. The system behaves normally from that point on, with the exception that the restore function is inoperative –from both a backup file or a rescue disk. Obviously, the startup process spans both the original and the new drive, but I cannot sort things out so that the operating system starts from the new 950 drive independently. After a week of frustration, I really, really hope someone here can diagnose what's going wrong in the startup process and 2 explain how to fix it.
The first image below is the disk management panel, and the second is the File Explorer view of the 840 (original) drive files. The third image is the Explorer view of the C partition on the C: drive, and the last is a shot of the contents of the "Data" partition on that drive.

Siw is right. You need a driver for 951 NVME.
You should insert the driver into your Win 7 Installation disk to be able to do a clean install and maintenance. Read my tutorial. Create a Windows 7 USB flash installation with new drives for new MB's

I've had installed a SM951 AHCI PCIe SSD drive. It gave me so many issues (without any real speed gain) that I've replaced it with a 850 PRO SSD SATA disk. Sata=RAID and PCIe M.2 drive problems

I'm interest on your opinion about the SM 951 as soon you get it running.

I've followed all the advice, including reinstalling the nvme driver.
I'm an ex usaf pilot and while I respect the knowledge of the board members, and appreciate any help, I am not comfortable with the "try this and see if it works " approach to solving problems. In my experience, it's better to diagnose a problem and correct the specific cause, rather than trying the most probable solutions one after the other, hoping to make things better before you screw them up beyond repair.
My windows system files are on a different drive than the boot partition, and I suspect the mbr is the root of the issue, not the nvme drive per se, but if I fix it before I give up and do a clean install, I'll post the cause(s).
Again, I mean no disrespect to anyone, and appreciate any suggestions.

Looking at your Disk Management screen print in post #1,
Your Disk 1 D partition is the System, Active partition, so that's where the bootloader was used to start Windows.
Your Disk 0 Data (no letter) partition is Active, but it is not the System partition, so the bootloader there is not used now.

I understand your concern about not wanting to try things and make matters worse, that's good.

All of the folks here trying to help you are giving the best advice they can.
All of us have made mistakes and hopefully figured out how to fix them, and learned from our mistakes.

If you are going to try and fix issues yourself, learn to use System Image backups, so you can recover.
I use Macrium Reflect free, and recommend it.

I think you need to somehow move the bootmgr from Disk 1 D to Disk 0 Data (no drive letter) partition.
Here is a tutorial, you can look at it and see if you want to try this:
Bootmgr - Move to C:\ with EasyBCD

Your situation is different than the tutorial, so you need to take your time to read and understand this.
You might need to (temporarily) add a drive letter to the Data partition to move the bootmgr.

You used the Samsung data migration tool, can you ask Samsung support to explain this ?

Thank you all for your advice. You are correct, two or three years ago I cloned an original Windows 7 installation from a hard drive onto the Samsung 840. and it would have saved me an enormous amount of time if I had simply done a clean install on the 951 – I just didn't want to go through reinstalling all my applications again. At this point, it's almost a matter of pride not to give up making this work. And even if it doesn't, I've learned a hell of a lot about the boot process that I wouldn't otherwise have delved into. Nearly as fun as EMM386 and HIMEM.sys, so thank you.
I've spent most of today reading up on the MBR, bootmgr, and winload, and it's going to take me a while to digest everything that's been provided here since my last post. I think I've gained a certain appreciation into how the MacBook Pro managed to gain a foothold.

Couldn't face the stress & delay of figuring this out on yet another machine.

Followed DavidE advice, bought EasyRE.

Booted ISO, it started it's Linux recovery environment, did lots of stuff, problem fixed, machine now boots. :)

It appears to check for many permutations and combinations of messed up settings & drivers, then automagic fixes them.

Great, now I don't have to understand all that arcane windows trickery & cludginess.