To turn on Windows Defender in Windows 8, navigate to the Start Screen, click the Search icon, type "Windows Defender" in the box, click on the program's icon, click on the Settings tab, and check the Turn On Real-time Protection box. Click the Updates tab, and check for any updates.Continue Reading
From the desktop screen, move the mouse pointer to the upper-right corner, and move it down. Click on the Start icon from the menu that appears along the right edge of the screen.
In the top right corner of the Start screen, click on the Search icon, and type "Windows Defender" in the box.
In the search list, click the Windows Defender icon.
Click on the Settings tab, and check the box next to Turn On Real-time Protection (Recommended). Click the Save Changes button, which is located at the bottom of the window.
Since the software was disabled, you should check for security updates manually. Click the Update tab and then the Update button, which is located in the middle of the window.
Return to the Home tab, and select Full from the list of scan options. Click Scan Now to perform a scan of your computer.