Windows 10: Why is my Win Defender gone?

I've had a few updates this wk. Didn't notice until today that Win Defender was gone after I had this popup below freeze me up. I do not have Norton installed. Should I download another Defender; I thought it was a default program?

:)

 

Why did the startup window get cleared?

I didn't missed any step, the list was gone and gone , even after using lot of programs the programs were not listed in that list.

 

Can't run Windows Defender

Win Defender Security Centre lists my Virus and Threat Protection as disabled. The message reads "Your Virus & threat Protection is managed by your organization."

This happened a month ago and was resolved when I thoroughly removed Malwarebytes, though it and Win Defender had co-existed without trouble for some years. Now Malwarebytes is gone, no other antimalware software in place. Anyone suggest what could be
disabling Win Defender?

 

win 10 defender issues

Hi,

Windows Defender helps in making your computer secure from any viruses or malware. Listed below are some reasons why the program will not work properly:

• Software conflicts (usually cause with other anti-virus application)
• Virus and malware infection
• Corrupted system files

To help you with the issue, we suggest following the steps provided by
PrashantKumar96 on this thread
that can help in running your Windows Defender successfully.

Let us know if you have other concerns.