I have a Lenovo Thinkpad Edge E520 (Windows 7 upgraded to Win 10 a couple months ago). Since I stopped a couple processes from running in Task Mgr (Message Control Plus, Windows 10 Upgrade Assistant), on startup I get a screen with Windows logo and circling dots under it (wait symbol), then the screen goes blank and I get a black screen with the circling dots. I let it run like this for 2 hours and it just stayed on this screen. I followed the procedures and ran Tweaking (attached) but no change. Sometimes, but not always I can press F5 while booting and get to Safe Mode and I think it actually booted correctly with F5 once or twice. Sometimes I can get it to boot normally when pressing F8 during bootup. When Safe Mode opens I get an error message "Get Started can't be opened by the Built-In Administrator account. Sign in with a different account." Another error message often occurs at this point, "Windows Security Center can't be started."
One other thing, not long before this problem began I installed drivers, help, support, etc. for an HP wifi printer. I have since uninstalled it with no benfit.