Windows Defender is the anti-malware component included with all Windows versions starting with Windows Vista. Like any software product, however, Windows Defender may run into unexpected problems, become unstable or refuse to even start. To try potential solutions, check out the guides outlined below.
To turn on the real-time protection provided by Windows Defender, start by pressing the Windows and Q keys on your keyboard. In the search field, type Windows Defender and press Enter. Open 'Settings' and check the 'Turn on real-time protection' option. Keep in mind that Windows Defender may have turned itself off automatically due to another cybersecurity product being present on your computer. This behavior is intended to avoid any potential conflicts.
Users encountering issues with Windows Defender also may want to check if any Windows updates have been released. Newer updates oftentimes resolve compatibility issues, fix known bugs and deal with security vulnerabilities. To check for updates, go to the 'Start' menu, select 'Settings,' and navigate to 'Windows Update.' Click on the 'Check for updates' button.
If nothing has been able to fix the problem, try to reset the Security Center service. Open the Search box on the taskbar and type services.msc in it. Open 'Services.' Navigate to the 'Security Center' service. Right-click it and select 'Reset' from the available options. Now, restart your computer and check if Windows Defender is working normally.