Question: Edit: Thank you to everyone, who helped me! In the end I decided to go with the brute force method and just installed a fresh OS (Windows Media Creation Tool) on the SSD and keep the HDD until I carry all apps I need from it to my SSD. To those, who might have a new drive and some files on the old one, just be aware that some programs on the old drive won’t work, because they can’t find their registry keys (I couldn’t open Steam from the HDD for instance and just had to install it new aswell).

So, hello…

I got a new Samsung QVO 860 1TB SSD yesterday to accommodate my Toshiba 1 TB HDD and have been having huge issues with cloning the contents of the hard drive to the SSD.

Firstly, I tried using the EaseUS TODO tool to:
a) Clone the WHOLE disk (Yes, every
partition …)
b) Migrate just the OS, which ended upcopying the whole C drive anyways,since I had everything on there

Both yielded the “Reboot and Select proper Boot device” error, when loading up the SSD from BIOS. In both cases I still had the Windows Boot Manager set as my primary boot option and then my HDD. The SSD was only accessible through Boot Override. I was luckily able to boot from HDD.

That brings us to today. I downloaded the Samsung Data Migration tool, since I have a Samsung SSD afterall, and started cloning the HDD to SSD. Everything went fine (it took 3 hours), the SSD had every single file from the hard drive and the computer automatically shut down 20s after the cloning completion.

I then disconnected the HDD (power and data cable) and booted into BIOS with SSD only. To my surprise, there it was: The SSD was in the boot order along with the Windows Boot Manager. I tried to boot from the SSD, but it didn’t work, same problem as before – I thought that was weird. I then rebooted again and let it do its own thing. It booted to Windows safe and sound. Everything was amazing and in the same place as it was in the HDD.

“Great,” I thought, “let’s just turn the system off and plug in the HDD so I can wipe it for future use.”

I booted into BIOS just in case it doesn’t try to boot into Windows from the HDD, but the WBM wasn’t there anymore. “Weird,” I thought again. Hopeful, I proceed to boot from the SSD… nothing. HDD maybe? It worked before… nothing.

On both the SSD and HDD I got the “Reboot and insert proper Boot device” error. Get this – I can ‘t even boot into Windows anymore, even with my HDD!

I scattered everywhere for an answer and did all I could:
a) Set optimized defaults in BIOS = Noresult
b) Disconnect the SSD, try to bootfrom HDD only = No result
c) Disconnect the HDD, try to bootfrom SSD only = No result (Really? Itworked a minute ago!?!!)
d) Load EFI Shell = No result

I really need your help on this one and I feel like I already know the answer. I think the boot record on both drives got corrupted in some way.

One thing to mention: Both drives are GPT based, so no conflict should be there.

Answer:a) Clone the WHOLE disk (Yes, every
partition …)

First mistake, you should not clone the drive, even more so with other partitions. You’re advised to not partition the SSD unless it’s partitions that the OS had created. Speaking of OS, if the OS was on the HDD, you should’ve reinstalled the OS from scratch.

b) Migrate just the OS, which ended upcopying the whole C drive anyways,since I had everything on there
Yeah, install the OS afresh, problem will be solved. You should remove the partitions on the SSD if they are storage media files since that will only degrade the SSD faster or worse make it run slower than advertised.