Hi,
Perform Reset and see if it helps.
a: Press Windows logo + W to open the search box.
b: Click Settings and then type Remove Everything and reinstall windows, hit enter.
c: Click Next
Note: Take a backup of all your data to an external disk, as the reset may result in data loss.
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Doesn't work with my system. I upgraded from Windows XP to Windows 7 to Windows 8, to Windows 8.1. Both Refresh and Reset options fail with errors about not finding files that are needed, even when the DVD is in the drive. I could just erase my computer using the installation DVD but it fails unless a previous version of Windows is installed, so am back to square one and aggravation again, for nothing. Worst of all, all my software is packed away during a major remodel so actually erasing my system is a bit out of the question, anyway. I have work to do besides and cannot lose any of the software I need to do that.
Microsoft just needs to get to the bottom of this problem and fix it. Taking away the system's rights and permissions to be able to read and set the lock screen and giving permissions only to TrustedInstaller is a bit on the ridiculous side, if you ask me. But, a permissions problem is at the root of this problem.