In response to the post of the av system not being able to turn it on that's make sure like 100% that another third-party software could have installed a antivirus that you might not be aware of some software's give you a antivirus software free bundled in other software's job first make sure that that did not happen most likely you have one installed then the other thing you should check is to make sure you have turned it on by typing window defender in the search box on your PC bottom-left then to have it activated online which gives you the benefits of being up-to-date on the time if this is not help you should consider looking how come you're not the administrator of the PC hope this helps you good luck
First of all I do have Admin priveleges logging in to my local account. Clicking on my icon in the Windows menu and choosing "Change Account Settings" shows that I am an Administrator.
Secondly while I appreciate your telling me that I probably have some other third party antivirus software installed, how can I find it ? Nothing shows up by name among the list of Apps that says anything about being a 3rd party antivirus program, and I have no recall that I ever installed such a program. While this is not directed at you at all, who are trying to help me, I find it incredible that Windows Defender Antivirus Service gives me an error code when I try to start it, there is no documentation what this error code means, and even if it means that another antivirus program is installed there is absolutely no indication what this program would be or even how the Windows Defender Antivirus Service even determines that this other antivirus program exists. So I am a little piqued about this sort of nonsense, of some obscure error code which nobody understands, still coming from Microsoft after nearly 30 years of Windows.
I do not see how I am supposed to activate Windows Defender Antivirus Service online, or even what good this is supposed to do me locally under Windows 10. Would you care to explain ? Other Windows Defender services, like the Windows Defender Firewall, are running fine.