To put it simply, this issue is possibly caused by the installation of third-party antivirus software, a corrupted registry, software conflicts, and so on. In addition to the case when Windows Defender could be turned off by group policy, some users said Windows Defender gets an unexpected error and cannot be opened or Windows Defender can't open after uninstalling Avast, Bitdefender, McAfee, AVG. One Windows 10 user from tomsguide said: 'A few days back I turned it off completely using group edit policy, but now when I try to put on the real-time protection slider, it asks for permission but then nothing happens.' tomsguide However, many users have reported that their Windows Defender can't be turned on for virus defense in Windows 10/8/7 when they click on the Turn on button. Once it scans and finds potential threats, this program will stop them. It can offer real-time protection from various threats like spyware, malware, and viruses to your PC.

Windows Defender (also called Windows Defender Security Center in Windor later), a fully integrated part of Windows, is an antivirus program. Windows Defender Will Not Turn on Windows 10/8/7

Use MiniTool ShadowMaker to Protect Your PC from Viruses and Other Threats.

How to Repair Windows Defender Windows 10/8/7.

Windows Defender Will Not Turn on Windows 10/8/7.

Windows defender not turning on