Windows Defender Error Code: 0x8050800d

Question

Been having some issues since the Windows 10 Anniversary update. Just install the fix to solve all the issues but now my Windows Defender WILL NOT turn on.  I keep trying to turn it on but directs me to uninstall other antivirus software that I DO NOT have on the computer. It does update the definitions but will not turn on the Real-Time Protection. The error message that I keep getting is 0x8050800d

Answer 1

Been having some issues since the Windows 10 Anniversary update. Just install the fix to solve all the issues but now my Windows Defender WILL NOT turn on.  I keep trying to turn it on but directs me to uninstall other antivirus software that I DO NOT have on the computer. It does update the definitions but will not turn on the Real-Time Protection. The error message that I keep getting is 0x8050800d

You did try a restart of the computer I presume?

The behavior you are describing is typical if there are remnants of a third party program interfering with Windows Defender.  This may occur even if WD was working okay before the not so Great Anniversary Update.

Go to Security and Maintenance, look in 'Security' and see what program is listed under Virus Protection.  Windows Defender will not be enabled if there is a program other than Windows Defender listed.

Think back to what other antivirus programs have been previously installed. Do you remember which AV product came pre-installed on the computer?  Maybe McAfee or Norton?  Try running the removal tools for any AV program that has ever been on the computer and then reboot...then try enabling Windows Defender.

See List of anti-malware product removal tools

Have you tried the steps recommended in Problems starting Windows Defender in Windows 8/8.1/10 ?

Or

See if the following might help you resolve the problem: 

http://www.thewindowsclub.com/enable-start-windows-defender

http://www.tenforums.com/tutorials/3569-windows-defender-real-time-protection-turn-off-windows-10-a.html

http://www.bleepingcomputer.com/forums/t/592660/windows-defender-turned-off-in-windows-10-cant-turn-it-on/

Alternatively - - -

You can consider a reset which will essentially be a “clean install” of Win 10 but you’ll lose installed programs and data/pics/music that is on the computer. https://support.microsoft.com/en-us/help/12415/windows-10-recovery-options

Or you can install a third party antimalware program (doing so should disable the real time protection of Windows Defender) and use the third party program for your antivirus protection. 

Choosing an Anti-Virus Program  

Is Windows Defender The Best For Windows 10?  Good article but ignore the ads.

http://www.dslreports.com/forum/r30380692-AV-Poll-2015

http://windows.microsoft.com/en-US/windows/antivirus-partners#AVtabs=win10

Good luck...