Disabling App Readiness service does indeed solve this problem, (no need for a clean boot)
ASKER
Windows 10 is a personal computer operating system featuring the "universal application architecture" (UAP); apps can be designed to run across multiple devices with nearly identical code, including PCs, tablets, smartphones, embedded systems, Xbox One, Surface Hub and HoloLens. Windows 10 also includes a virtual desktop system, a window and desktop management feature called Task View, the Microsoft Edge web browser, support for fingerprint and face recognition login, voice-based search (Cortana), new security features for enterprise environments, and DirectX 12 and WDDM 2.0 to improve the operating system's graphics capabilities for games.
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The symptom "black screen with mouse pointer" is clear: the process explorer.exe does not start.
You can simply call task manager by pressing CTRL-shift-Escape together and then run a new process: explorer.exe
Afterwards, if that worked, we can look at the system. Maybe you have another user to try with - that should be done.