After recent Windows Update series of 5/9/2015, certain Windows 8.1 64-bit security features were broken. Now at logon screen my mouse is blocked, the pointer is moving but clicks aren't processed. I can only navigate by keyboard Tab button to select a user account and login. After login there's no access to desktop or Taskbar. Only after clicking Ctrl+Alt+Del, and then Cancel to return back I can access desktop or Taskbar buttons by mouse. When I open IE11, scrolling is blocked on any webpage, and full reset of Internet Options doesn't fix it. Only after Signing Out and signing back to the account I can work normally, and IE11 works OK too.

This happens with any user account. I setup a new local account, and the same thing happen again at 1st login. It also happens on another install of Win 8.1 on the same PC (dual boot) right after reboot to finish install of the same Windows Update, and that install was clean of 3rt party programs and GPU drivers. During 5/9/2015 a number of Windows KBs were installed, and the following 5/12/2015 series of updates didn't fix that problem.

This problem happens also in Clean and Safe boot modes, with or without 3rd party or Microsoft antiviruses installed or running. I run System Maintenance, also sfc / scannow and DISM file checks & repairs, some files were fixed, now these checks show no errors. But the security issue was not fixed. Right now the only way I can work on a PC is Ctrl+Alt+Del+Sign out and sign in back to the same or different user account. At 1st sign in access to many things is blocked in any mode, including Charms Bar when moving mouse to the right corners, but it opens with keyboard shortcuts.

All these issues may be linked to Windows Explorer broken security settings. I can obviously try to reinstall or repair Windows, but after installing the same updates its likely going to happen again. Pls suggest what to search for in error logs, and how I can pinpoint and fix some files, or Registry & security settings to re-claim my PC hijacked by Windows? As you know, reinstalling Windows is not the best idea or common cure, especially if its broken by own updates, and requires reinstalling all 3rd party software to no avail, and with the same expected outcome. :) 

Any way to reset Windows security settings to defaults?

• Edited by sambul13 7 hours 59 minutes ago