Having trouble getting windows defender to start even though it's set to auto-start? Is your antivirus not being detected in Vista? I had this problem in Vista Home Premium 32-bit and none of the suggested suggested:
Seems like this is a problem with the Windows Repository somehow being corrupted. I had AVG installed on this system previously and somehow uninstalling created problems. A good writeup was found here and a screenshot based repair is given here:
But even these solutions didn't work. So here's what I did. Warning: Expert Windows users only should try this.
1. Run sfc /scannow from an elevated (adminstrator) command prompt (right click on command prompt icon and choose run as administrator after typing cmd.exe in the start search box).
2. If sfc returns an error message about corrupted files, you'll need to check the cbs.log
3. CBS.log viewing: navigate to c:\windows\logs\CBS from the computer icon and copy the file and paste. Open the copy of the cbs log in notepad and search for "cannot repair"
4. In my situation, it was the wbemsvc.dll file that was corrupted and could not be repaired. Luckily I had another HP laptop so I copied the file from the c:\windows\system32\wbem folder into the c:\ of the affected laptop
5. Now the system32 file cannot normally be replaced so reboot into safe mode and run a safe mode command prompt
6. cd c:\windows\system32\wbem
6. run the following commands: takeown /f wbemsvc.dll
7. That will give you ownership of the file, but you still have no rights to delete it. Now you can run the cacls command to give yourself full control rights to the file:
8. Type the following - Replace USERNAME with your username which will be shown after the first command succeeds: cacls wbemsvc.dll /G USERNAME:F
9. Copy the good dll from the c:\ to this location and overwrite: copy c:\wbemsvc.dll
10.Issue a exit command and reboot the system