The above issue, commonly occurs if you have installed a different security product on your system, but you have decided to return back to the default Windows security protection ('Windows Defender' on Windows 10 & Windows 8 or 'Security Essentials' on Windows 7). But some users reported that when they click the Antivirus Protection – Turn ON button in Action Center (in Windows 10: Control Panel > Security and Maintenance), Windows Defender will not start but instead the system opens at 'C:\Windows\System32' folder. In a previous tutorial I had described the way to enable Windows Defender on your Windows 7, 8 or 10 based computer.
