I ran into error while reinstalling Microsoft Windows 10 Pro on Lenovo T420 laptop. The computer restarted unexpectedly or encountered an unexpected error. Windows installation cannot proceed... Workaround Press SHIFT + F10 to open Command line windows. Run regedit.exe to open Registry Editor Go to Computer\HKEY_LOCAL_MACHINE\SYSTEM\Setup\Status\ChildCompletion Look for Setup.exe on the right pane Doubleclick on Setup.exe on the right pane, change Value data from 1 to 3, press OK. Press OK again to close Install Windows dialog. Reboot. The installation will continue.