I cloned Windows 10 from a HDD Partiton into an SSD Partition. The SSD has 2 Partitions: one (1st) is Windows 7 (manually installed) and the other is the cloned Windows 10 from previous HDD. I created the entry in Boot Menu, transfered the Boot Menu to SSD onto Win 7 Partition. Computer boots, a Win7 styled menu appears (black menu with multiple OS choices). I can select any but Windows 10 does not procede to the User Login even if it loads, just a black screen appears and a responsive cursor with loading style. The computer experiences high CPU load. I have created a Windows 10 bootable stick. But this one does not have a Repair Menu just to install a new copy.
Edit: Converted the old style Bootmenu to the Windows 10 bootmenu which gives an option to troubleshoot Windows 10.
Best Answer
I found the workaround myself. There were the drive letters that caused the trouble. Booted the cloned Window from SSD via Troubleshooting and F6 as Safe Mode with Command Prompt. Typed CTRL + SHIFT + ESC and then observed something strange. The instance actually booted the Windows from the HDD that is in the Caddy and everything was mounted as C:. But not so did the Command Prompt where it initiated D:\windows\system32 instead of C:\windows\system32. In other words the CMD instance thought it is the cloned Windows in SSD which is active. I then entered regedit from CMD, removed all the entries in HKEY_LOCAL_MACHINE\System\MountedDevices but left the empty (Default) Value. Removed the HDD with the Caddy which is hotswappable, rebooted the system. Selected the cloned Windows 10 from SSD and to my amazement it kicked in. The MountedDevices automatically had created a new entry with current Drive (SSD) and current active Partition being correctly C:
Caution: Messing with Registry may damage your Windows!
Image of the new entry, Initial Path and Drive Uniqueidentifier