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  1.    15 Nov 2015 #1
    Join Date : Oct 2015
    Posts : 65
    Windows 10 Pro

    Cannot start Windows Defender: Error 0x800705b4


    Hello,

    Today I was warned by windows 10 that my antivirus was off. I checked windows defender (the only AV I have) and it was indeed off. However when I try to start it I get an error:

    Click image for larger version. 

Name:	1.png 
Views:	4 
Size:	133.5 KB 
ID:	48253

    So then I went to services and tried to manually start the service, only to get this:

    Click image for larger version. 

Name:	2.png 
Views:	6 
Size:	59.4 KB 
ID:	48254

    Does anyone know what is going on here? Why does the service keep getting turned off?

    Any help is appreciated!
      My ComputerSystem Spec
  2.    15 Nov 2015 #2
    Join Date : Oct 2014
    In a house with a crazy cat trying to kill me
    Posts : 17,348
    Win 7 32, Win 7 64 Pro, Win 8.1 64 Pro, Win 10 64 Education Edition

    I had that happen in the past & sometimes running the update fixes the problem. Click the update tab & update Defender defs.

    You could run an SFC to see if anything needs fixing.

    SFC Command - Run in Windows 10 - Windows 10 Forums

    Then there is always the possibility that you have a virus on your system that's preventing the launch of it. You might want to run a scan with Malwarebytes or AdwCleaner just to be on the safe side. The free version of Malwarebytes will work fine.

    There is a fix listed here for 8, it should apply to 10 also.

    http://www.thewindowsclub.com/error-...ndows-defender
      My ComputerSystem Spec
  3.    15 Nov 2015 #3
    Join Date : Oct 2015
    Posts : 65
    Windows 10 Pro
    Thread Starter

    Hello Borg 386

    Thanks for the suggestions. Before I made this thread I had already tried sfc/scannow, as well as run malwarebytes.

    The registry fix actually doesn't work No such entry exists!

    Edit: I just tried to confirm that windows defender was up to date and now I have another problem...

    Click image for larger version. 

Name:	update error.png 
Views:	2 
Size:	24.4 KB 
ID:	48423
    Last edited by Ocman76; 15 Nov 2015 at 19:03.
      My ComputerSystem Spec
  4.    16 Nov 2015 #4
    Join Date : Apr 2015
    Posts : 12,942
    W10Prox64

    Hi.
    As @Borg 386 said, the registry key fix should do it. If the key is not there, no problem - it says:
    Alternatively, you can delete the Windows Defender key
    HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
    from the left pane of the image shown in step 2. Finally, reboot the system

    (I suppose you could also create the key, and set the value = 0)

    So, after rebooting the machine, is the problem still there?

    If so, you may have an infection. If sfc /scannow reported no integrity violations, then you might try an ESET online scan.
      My ComputerSystem Spec
  5.    16 Nov 2015 #5
    Join Date : Apr 2015
    Posts : 12,942
    W10Prox64

    One other thing I found, and this may or may not help:

    Possible corruption of the .Net Framework
    There is a Fixit mentioned in this post
    Error Codet install - Microsoft Community

    Someone also points to this thread with instructions on how to manually update the definitions, which, once completed, seemed to have resolved the problem.
    How To Manually Update Windows Defender Definitions - Anti-Virus and Anti-Malware Software
      My ComputerSystem Spec
  6.    16 Nov 2015 #6
    Join Date : Oct 2014
    In a house with a crazy cat trying to kill me
    Posts : 17,348
    Win 7 32, Win 7 64 Pro, Win 8.1 64 Pro, Win 10 64 Education Edition

    Something I forgot to include. you need to run SFC at least 3 times to make sure it fixes everything, it doesn't always get everything on the 1st or 2nd time. This info is listed under option 3.

    If SFC could not fix something, then run the command again to see if it may be able to the next time. Sometimes it may take running the sfc /scannow command up to 3 times with Fast Startup turned off and restarting the computer after each time to completely fix everything that it's able to.

    If not, then run the Dism /Online /Cleanup-Image /RestoreHealth command to repair any component store corruption, restart the PC afterwards, and try the sfc /scannow command again.
    Also, good idea simrick. I seem to remember in the past when Defender or Security Essentials would hang up, I applied the updates manually & that fixed the problem in some instances.

    I'm seeing references to that same code being an update error.

    Fixing Windows 10 Update Error 0x800705b4 | The Generalist IT

    OK, I know this is is a shot in the dark, but have you tried turning it completely off & then back on? I've seen instances where a program shut completely off & then back on sometimes fixes it. Worth a try maybe....

    Windows Defender - Turn On or Off in Windows 10 - Windows 10 Forums
    Last edited by Borg 386; 16 Nov 2015 at 10:08.
      My ComputerSystem Spec
  7.    16 Nov 2015 #7
    Join Date : Oct 2015
    Posts : 65
    Windows 10 Pro
    Thread Starter

    Thanks for all the suggestions guys. I'm at work right now, but il give these all a shot when I get home later today.
      My ComputerSystem Spec
  8.    16 Nov 2015 #8
    Join Date : Nov 2015
    Posts : 1
    Windows 10

    Quote Originally Posted by Ocman76 View Post
    Hello,

    Today I was warned by windows 10 that my antivirus was off. I checked windows defender (the only AV I have) and it was indeed off. However when I try to start it I get an error:

    Click image for larger version. 

Name:	1.png 
Views:	4 
Size:	133.5 KB 
ID:	48253

    So then I went to services and tried to manually start the service, only to get this:

    Click image for larger version. 

Name:	2.png 
Views:	6 
Size:	59.4 KB 
ID:	48254

    Does anyone know what is going on here? Why does the service keep getting turned off?

    Any help is appreciated!
    Try step 7 in this guide: Windows Defender Does Not Start in Windows 10 - WindowsInstructed

    Worked for me
      My ComputerSystem Spec
  9.    17 Nov 2015 #9
    Join Date : Oct 2015
    Posts : 65
    Windows 10 Pro
    Thread Starter

    Alright, sorry for taking so long to get back, I have been working for hours to get through all these suggestions.

    1. I have added the registry entry and set the value to 0. After rebooting, no luck.

    2. I did the ESET online scan and it found nothing. I have also done an offline microsoft scan that found nothing. I am 99% sure I don't have any virus.

    3. The link to repair the .Net framework doesn't work (it doesnt apply to windows 10). Is there any way to repair the .Net framework in windows 10?

    4. I am unable to manually update windows defender definitions. I download the mpam-fe.exe from the microsoft link but running it doesnt do anything? I even have tried running it as administrator, my pc thinks for a couple of seconds and nothing happens...

    5. After running sfc/scannow a second time it claimed it found integrity violations but was unable to fix them. I tried the Dism cleanup command, restarted the computer and tried the sfc again. Still couldn't fix the problems. Would you like me to upload my CBS log here?

    6. I tried the link about the update error. Windows update still refuses to download the latest definitions. It doesn't give any error message anymore. It just says its having trouble and to restart my device, which I have tried and doesn't do anything.

    7. I have tried turning off windows defender, restarting, turning it on again, and restarting. No change

    It seems to me like a bunch of stuff is screwed up with my pc right now. I have another separate thread currently open regarding issues with windows search indexing not working. All of these issues appeared right after I upgraded to the new windows build (10586) a couple days ago. I kind of wish I stayed with windows 7...
      My ComputerSystem Spec
  10.    17 Nov 2015 #10
    Join Date : Apr 2015
    Posts : 12,942
    W10Prox64

    In-place upgrade/repair? What do you think @Borg 386?
      My ComputerSystem Spec

 
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