You can't install Windows while connected to your PC via external enclosure and then use it in his laptop. Windows will install and configure the operating system and drivers for an entirely different chipset and storage controller, among other hardware like the network adapter and other drivers. It just won't work that way.
The drive NEEDS to be installed in the unit it is going to be used in when you do the installation. Doesn't matter if it is "slow" or not. That is where it needs to be. Otherwise you will have an OS installation that is botched and bungled from the start, if it even works, which it probably wont' because the Windows boot manager and EFI partitions will likely not be compatible after creating the installation connected to a different PC.
SFC Scannow works for ALL versions of WIndows 10, but I would recommend running DISM before running SFC Scannow for any system that NEEDS to have SFC Scannow run.
See here:
Run DISM first, SFC Scannow second.
You should try to fix the problem before you nuke your Windows installation.
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Run the DISM Command to Fix SFC Problems
You shouldn’t normally have to run the DISM command. However, if the SFC command fails to run properly or can’t replace a corrupted file with the correct one, the DISM command—or System Update Readiness Tool in Windows 7—can sometimes fix the underlying Windows system and make SFC run correctly.
To run the DISM command in Windows 8 and 10, open a Command Prompt with administrative privileges. Type the following command and then press Enter to have DISM check your Windows component store for corruption and automatically fix any problems it finds.
DISM /Online /Cleanup-Image /RestoreHealth
Allow the command to finish running before closing the Command Prompt window. This may take five to ten minutes. It’s normal for the progress bar to stay at 20 percent for a while, so don’t worry about that.
If the results of the DISM command state that anything was changed, restart your PC and you should then be able to run the SFC command successfully.
On Windows 7 and earlier, the DISM command isn’t available. Instead, you can download and run the
System Update Readiness Tool from Microsoft and use it to scan your system for problems and attempt to fix them.
After running the DISM, run SFC Scannow.
At the Command Prompt, type the following command and press Enter to run a full system scan and have SFC attempt repairs:
sfc /scannow
Leave the Command Prompt window open until the command completes, which may take some time. If everything is fine, you’ll see the message “Windows Resource Protection did not find any integrity violations.”
RELATED: How to Use Safe Mode to Fix Your Windows PC (and When You Should)
If you see a “Windows Resource Protection found corrupt files but was unable to fix some of them” message, try restarting your PC in Safe Mode and running the command again. And if that fails, you can also try booting with your installation media or recovery disc and trying the command from there.