Passive Mode

[Tom_798]

  I have Windows Defender installed on Windows 7 Home System.  I get a message when I try to turn on Defender.  I wanted to know if temporarily switching to Passive Mode & restarting computer "solve" the problem?  I get a message when trying to turn on Defender that states it is blocked by group policy & contact system administrator.  I am running computer as administrator & this edition of Windows 7 does not support the gpedit program (group policy editor). 

[DavidR]

When you install any 3rd party antivirus then windows disables windows defender to prevent two resident scanners being active and potentially conflicting.

Why would try install a 3rd party antivirus and then want to enable Defender ?

What is it that you are trying to achieve ?

[Tom_798]

  I would like to take a full scan using Defender & then turn it off immediately afterwards is all I'm try to do.  Thank you for quick reply.

[DavidR]

You should be able to run a scan with windows defender without having to enable it, as far as I'm aware it is only the on-access element that is disabled.

Though you have to have the Periodic Scanning switched on, see attached image.
This is on my windows10 system and I have mine switched off, image 1 click to expand.   You would have to check if this is an option on win7, which I don't use.

That said I don't know if that is available in win7, you could try a google search and see if/how you run a periodic scan.

Passive mode can be enabled within Avast if needs be, Menu > Settings > General > Troubleshooting, image 2.

[Tom_798]

   I found a temporary work around to be able to scan.  This work around may not work for more than a couple hours as registry will automatically reverse itself.  I opened regedit (registry editor) & run as administrator.  I then navigated to the left pane, navigate to the HKey_Local_Machine\\Software\\Policies\\Microsoft\\Windows Defender.
  Find DisableAntiSpyware key in the right pane and delete its value. For this purpose, you have to double-click on the REG –DWORD and set its value to 0.  I closed registry editor & was able to open Windows Defender. 
  Added note:  Turn off  Real Time Protection in Defender if using any other antivirus protection program on your device.