Windows 10: 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:





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





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

Any help is appreciated!

:)

 

Windows defender error code of 0x800705b4

I recently did a fresh, clean install of build 10130 (Mistake) but now windows defender will not start and I cannot turn it on. I get an error code of 0x800705b4, can anyone help?

<Modified Title by adding "error code of 0x800705b4" for clarity>

 

Can't turn on Windows Defender real-time protection.

I cannot turn on real time protection..error code 0x800705b4

Modified title from: Defender

Moved from Virus and Malware / Windows Defender / Getting Started and Upgrading / Windows 10

 

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

 

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 *Sad No such entry exists!

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

 

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 keyHKEY_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.

 

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

 

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.

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

 

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.

 

Try step 7 in this guide: Windows Defender Does Not Start in Windows 10 - WindowsInstructed

Worked for me*Party

 

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? *sarc 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 *Sad

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...

 

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

 

I think you should run it 3X like the tutorial suggests. Still a chance it can fix it. It may fix it on the 3rd try.

If not, agree simrick, time to try one of these. Indeed, if you are having various problems, doing a repair install could be the best option aside from doing a clean install. That's up to you, with a clean install you start with a fresh OS. However you do loose your setup, so the choice is up to you.

Repair Install Windows 10 with an In-place Upgrade - Windows 10 Forums

See the tutorial & at the bottom you will find links to the other options listed.

I see other people are having this prob, I wonder if it was caused by the latest updates?

 

I have ran the sfc command over 6 times now (restarting my pc in between)... its never able to fix the corrupted files.

The ironic thing about all this is that in order for me to install the new windows 10 build I did an in place upgrade.

I was not offered the new build in windows update because my windows 10 installation was less than 30 days old. I wanted the new build because I heard it might fix the DTS 5.1 surround sound bug (another windows 10 problem...). Not only has everything been screwed up since the new build, but 5.1 surround sound still doesn't work *Huh

I guess when I get home from work today I can try the in place upgrade again? Maybe it will work better this time...

If all else fails I will completely flatten my installation and do a clean reinstall by Christmas, im planning on getting a new SSD.

 

@Ocman76 if you'd like, copy and paste the following in an administrative command prompt and we'll have a look at your CBS log.

This will place a text file on your desktop called sfcdetails.txt. Upload it an an attachment and we'll have a look. There are one or two "problems" that are erroneous and will never be fixed by the system file checker, like an entry for a Canon printer...