Defender won't turn on

In Windows Security Center, it shows that Defender is turned off. When I
click to turn on, it searches for new defintions...but none are ever
found...and Defender will not turn on. However, in the Application Event
Log, there are numerous events with Defender as the source showing scans
being done each night along with other detection activity. I'm running Vista
Home Premium w/ NAV2007...both were pre-loaded on a new PC from Dell.

Any insight as to why Security Center shows Defender as off is appreciated
along with how to resolve.

I have this same problem. It is driving me crazy. Anyone found a way to fix this?

Please perform the following to resolve your issues.

Open elevated command prompt and type cd\windows\system32\wbem press enter

Then type ren repository repository.old and press enter.

Restart the computer and check your security center again hopefully
everything should be working there.

I recieved a " Access is denied" message when I followed these instructions.
I ran the command prompt as adminsitrator and recieved the same message.
Vista Home Premium.
Windows Defender will not turn on, and doesn't recognize Avast (free
version)

Simple All you need to do is

Start->Search type cmd and command prompt will show up->Right click->Run as
administrator and then type the commands as follows

Cd c:\windows\system32\wbem
ren repository repository.old press enter and reboot

If this doesn't help start the computer in safe mode and rename the folder
in safe mode.

If it still doesn't works turn off UAC and then try to rename it with
elevated command prompt in normal mode.

If it still doesn't works up then right click on the repository folder under
c:\windows\system32\wbem and go to properties ->Security Tab->Click
advanced->Ownership->Check replace owner on the subcontainers and
objects->Select your user name or administrators and click apply and then
OK(Twice)
Then click add (In the security tab) and then on the next window type
everyone and click OK.Ensure to give all permissions to everyone and click OK.

Rename the folder now.

I have the same problem. Thanks for the clear instructiuons.

I tried every step outlined in your post and still cannot rename the
Repository Folder.

After the last step to change owner and give everyone permissions, I still
get "You need permissons to perform this action" from Explorer or "access is
denied" from an elevated command prompt

Found this information

which suggests two ways to resolve this.

One is to stop Windows Management Instrumentation with

net stop winmgmt

before renaming the repository folder

then starting it again with

net start winmgmt.

This allowed me to rename the folder and once the folder was renamed, the
original problem of Security Centre and Windows Defender being incorrectly
reported as off was fixed.

Hmm..
Kindly confirm me who is the current owner of your repository folder.

Just confirming the correct procedure again

Right click ->Properties->Security tab->Advance Button->ownership tab

Further have you done an upgrade or it's a clean install?

Thanks and Regards

The owner was Steve\Administrator and this was an upgrade to Vista Business
from XP Professional SP2 with WIndows Defender already installed. However as
posted above stopping the Windows Management Instrumentation service allowed
the folder to be renamed which then solved the problem.

This worked for me, after rebooting, everything was turned on !
thanks alot.

Is the Defender service set to Automatic?

Snuffy wrote: Defender will not turn on when I boot up , but I have to turn
it on thru control panel.

Try this to manually install updates of windows defender, http://support.microsoft.com/kb/923159/. It should work!