How to turn on windows defender antivirus when not option shows to turn it on

1. Check whether another antivirus product is installed or still registered. On Windows 10 and Windows 11, Microsoft Defender Antivirus turns off automatically when another antivirus app is installed and turned on. If that other app is removed, Defender should turn back on automatically.
2. Try turning on real-time protection directly:
   • Open Windows Security from Start.
   • Select Virus & threat protection.
   • Select Virus & threat protection settings or Manage settings.
   • Turn Real-time protection to On.
3. If the Virus & threat protection page is missing the control, check whether Defender is being disabled by policy:
   • Open Services by searching for services or running services.msc.
   • Look under Windows Defender > Operational for Microsoft Defender Antivirus Service.
   • If the service starts and then immediately stops, that can indicate Defender was automatically turned off for compatibility with a non-Microsoft antivirus.
4. Check for policy settings that disable Defender:
   • Open Command Prompt as administrator.
   • Run:

          GPresult.exe /h gpresult.html
     

   • Open the generated gpresult.html report.
   • Check under Windows Components/Microsoft Defender Antivirus for Turn off Microsoft Defender Antivirus.
   • Also check for DisableAntiSpyware entries in policy results.
5. If multiple management methods were used, resolve policy conflicts. Microsoft recommends determining where Defender settings are configured and removing or revising conflicting policies. Using one management method gives the best results.
6. If a third-party antivirus was previously installed, avoid running two real-time antivirus products together. Microsoft recommends uninstalling the previous security software before relying on Defender.

If Defender still shows as off after the previous antivirus has been removed and no disabling policy is present, the supported guidance in the provided material is limited to checking Windows Security, Services, and policy conflicts.

• Microsoft Defender Antivirus in the Windows Security app
• Troubleshoot Microsoft Defender Antivirus while migrating from a non-Microsoft solution
• Antivirus and antimalware software: FAQ
• Windows Security App Overview
• Troubleshoot Microsoft Defender Antivirus settings