Windows Defender in Windows 8.1 Will Not Turn On

http://www.microsoft.com/security/pc-security/windows8.aspx

On Windows 8 when a third party antimalware program is installed the Windows Defender (WD) program is disabled.

If you wish to use WD on W8 you must uninstall the third party antimalware program, run the McAfee Removal Tool, Norton Removal Tool, etc  and reboot the computer.  List of anti-malware product removal tools

WD should then be enabled though you may need to start the program in Security Services.

For further information see

http://www.eightforums.com/tutorials/21962-windows-defender-turn-off-windows-8-a.html

Windows Defender on Windows 8 - Introduction and Frequently Asked Questions

After some gnashing of teeth and much lost hair, I solved this problem for myself.

It was a conflict with "Spybot - Search & Destroy"

To fix:

Open Spybot, go to Settings>System Services tab, and turn off the Security Center Service.

You can now restart Windows Defender. Turn Spybot's Security Center Service back on afterwards and have both programs running and checking for virus as well as malware.

http://blogs.microsoft.com/cybertrust/2014/08/05/can-i-run-more-than-one-antivirus-program/

MS does not recommend running other antimalware programs concurrently with Windows Defender on Windows 8.

You should never have more than one security product installed on the PC providing active protection/scanning. This can cause performance issues, system instability and conflicts between programs, and can hinder the effectiveness all installed antivirus products. Even if you attempt to have more than one product installed, with one active and another disabled, the disabled product will likely still have active components and/or drivers installed that will conflict with any other installed antimalware program. 

But it's your computer and your decision.....

Regards...

I am having this same issue. This is a new software rebuild with Windows 8.1 and no other virus or malware packages installed. 

Control panel reports the Windows firewall is on, the Action Center reports spyware protection and virus protection are turned off. Attempt to turn on via the action center and receive the following message: "Real-time protection couldn't be turned on. This operation returned because the timeout period expired." Error code reported was 0x800705b4.

The following steps have been taken (following additional research):

• Verified Time and Date settings are correct.
• Verified, via Services.msc, Windows Defender is set to automatic and is running.
• Attempted, via Regedit, to modify the setting in HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender. This recommendation illustrated how to change the data value for  DisableAntiSpyware, named *DWORD,*from 1 to 0. My data value was already 0, so did not need to be reset.

Can anyone offer any further suggestions?

Don

ok...I am computer dumb! My windows defender is OFF and MacAfee is on. I don't want  MacAfee and don't remember putting it on my laptop. I want defender back. But when I go to the action center ....it says MacAfee firewall is ON and defender is OFF. It wont let me turn defender ON because MacAfee is ON. But I don't know how to turn MacAfee OFF. ANd if u tell me how, then how do I get defender turned back ON????