
Microsoft started rolling out Windows 10 anniversary update early August.
So many users complained that after installation of the Anniversary Update, their Windows 10 froze, and they couldn't sign-in.
Microsoft has now announced a fix, The fix is automatically applied when installing the Windows 10 Anniversary Update. If you already have the Windows 10 Anniversary Update installed on your PC or tablet, then you can fix it by accessing the second administrator account. After you signing in, install the latest Windows 10 update and reboot the PC.
If you do not have the second administrator account, you can try one of the methods listed below.
First Method: Try uninstalling the Windows 10 Anniversary Update by using the Recovery Console. First go ahead and reboot the PC. When you get to the sign-in screen, hold the Shift key and the Power button simultaneously. The PC will restart, and on the screen choose
Troubleshoot >
Advanced Options >
Go back to the previous build.
Sencod Method: If the first method did not work for any reason, try using the
Settings from
Safe Mode. Reboot the PC, At the
sign-in screen,
hold the
Shift key and the
Power button continuously.
Your Computer will restart, choose
Troubleshoot >
Advanced Options >
Startup Settings >
Restart. After your Computer restarts, you will see a list of options.
Select
4 or
F4 to start your PC in
Safe Mode. Open the
Settings App in
Safe Mode, select
Update & Security >
Recovery Tab >
Go back to an earlier build.
Click on the
Get Started button under "
Go back to an earlier build" and follow the instructions.
That's all

After uninstalling, reinstall the latest Update from the Windows 10 download page. Before reinstalling, make sure you back up your data, just encase you encounter problems.