How to fix error code 0x800705b4 when starting Windows Defender?

When starting Windows Defender, error code 0x800705b4 typically indicates that the service is not enabled. This can happen if Defender is turned off in Windows Security, or if it's been disabled by another program. Error code 0x800705b4 can also occur if Defender's definitions are outdated, or if the service is experiencing an issue.

• Try running the Windows Defender Troubleshooter
• Try updating your virus and spyware definitions
• Try running a full scan with Windows Defender
• Try resetting the Windows Defender settings

1. Try running the Windows Defender Troubleshooter

1. Open the Start Menu and search for "Windows Defender"
2. Right-click on "Windows Defender" and select "Run as Administrator"
3. In the "Windows Defender" window, click on "Troubleshoot"
4. On the "Troubleshoot" window, click on "Scan"
5. On the "Scan" window, select "Windows Defender" from the "Threats" list and click on "Scan"
6. On the "Scan" window, click on "Next"
7. On the "Next" window, click on "Advanced"
8. On the "Advanced" window, click on "Scan Options"
9. On the "Scan Options" window, click on "Confirm"
10. On the "Confirm" window, click on "Scan"
11. On the "Scan" window, click on "Next"
12. On the "Next" window, click on "Results"
13. On the "Results" window, click on "Next"
14. On the "Next" window, click on "Fix"
15. On the "Fix" window, click on "Next"
16. On the "Next" window, click on "Finish"
17. On the "Finish" window, click on "Close"

2. Try updating your virus and spyware definitions

1. Open the Windows Defender Security Center.
2. Click on the Virus & Spyware Protection link.
3. On the Virus & Spyware Protection page, click on the Update tab.
4. On the Update tab, click on the Check for Updates button.
5. On the Check for Updates page, click on the Download and Update button.
6. On the Download and Update page, click on the Install Updates button.
7. On the Install Updates page, click on the Install button.
8. On the Installation Results page, click on the Close button.
9. Restart your computer.

3. Try running a full scan with Windows Defender

1. Open Windows Defender.
2. Click on the "Scan" tab and select the "Full Scan" option.
3. Click on the "Start Scan" button to start the scan.
4. Wait for the scan to complete.
5. If the scan results show that there is a problem with the Windows Defender software, then click on the "Fix Issues" button to try to fix the issue.
6. If the issue is not fixed, then click on the "More Information" button to get more information about the problem.

4. Try resetting the Windows Defender settings

1. In the Start menu, type "regedit" and press Enter.
2. In the Registry Editor window, click the "HKEY_LOCAL_MACHINE" key.
3. In the " hive " window, under the "System" key, click the "Windows Defender" key.
4. In the "Windows Defender" key's "Default" subkey, delete the "DisableAntiSpyware" value.
5. Close the Registry Editor window.
6. Start Windows Defender and click "Scan Now" to run a scan.
7. If Windows Defender detects a malicious threat, it will display a message recommending that you install the latest antivirus software. If you do not have the latest antivirus software, you can click "Protect Now" to install it.

If you didn't find success with an option above, then try:

1. Try disabling any third-party antivirus software you are using
2. Try uninstalling any recently installed programs
3. Try running the System File Checker tool
4. Try running the DISM tool