Good Morning Suat,
Found that post from Don. Note, get the VM off the OS drive as Pauli mentioned, just asking for trouble if something goes wrong. I keep a separate 1TB HDD for my 8 vm's, nothing else. On the new machine, will transfer those vm's to a NVMe since originally bought a 970 for the OS, picked up a deal with a 980, that was not available at the time, as now using 11th Gen CPU for the extra bandwidth lanes.
In VMware, I can copy the vm to another location from a offline backup. When first loading, VMware asks if this vm was copied or moved. select moved, then it proceeds to load and keeps activation. I have even done this using a different Host system, the vm still activated. It would not activate using the copy option (default). But this is in VMware.
This should help you backup the vm for worst case scenario. I clean install several times a week, depending on MS, using existing vm's, and they all activate as soon as I put them online. just like a real computer. Good luck, and enjoy the learning curve.
Thanks Don for clarification. This time made a backup for my notes.
I have some Hyper-V VMs that have a digital license for Windows 10 Pro. These were originally activated using the Windows Insider Product Key in early 2015. Although that Product Key can no longer be used to activate a new VM, the VMs that I have are still on the same host PC as I have had since 2012. I only need to keep a copy of the small VM files (excluding the VHDX disk file) to maintain the activation status of these devices, so I keep a copy of these small files in a OneDrive folder for backup.
I can clean install my host PC, import the VM files and still they retain their Windows 10 digital license if I install Windows 10 Pro on them.
You might be able to troubleshoot the boot issues of your VM, just as we could with a physical PC. However, it would be simplest to just clean-install Windows 10. As was said in Johnny_55's first reply, as long as the VM files are preserved, the virtual machine's Hardware ID should ensure that it will auto-activate Windows 10 once you bring it online. The files representing the VM's "hardware" for the Windows 10 digital license are the .VMCX .VMGS and .VMRS files, plus an empty folder by the same name as the 3 files. Most of mine are only about 4 MB in total size, per VM.
You can always just keep the current VHDX disk file intact and create a new file to test if it will auto-activate. Create a new file and clean install Windows 10 to it. Use the same Edition as you have the license for, which was the upgrade from Windows 7 retail. You should not need to login using a Microsoft Account to see successful activation, since it is based on the device's HWID, as recognized by the Activation servers.
Don
Regards,