Some Strange Things Going on With Defender

This has been going on for so long now I think I may have some sort of malware.

I have a red cross on anti virus in security centre and on the task bar shield. In settings it tells me I am using third party anti virus but I have used every dedicated AV uninstaller.

I have also visited services.msc and the registry and checked that all is as should be there. In services you can start Defender but it doesn't "stay started" as it were.

Despite telling me that I am using 3rd party AV, update still tries to download new virus definitions for defender, and of course they fail. As they have been since Dec 14th last year when coinicidentally Security update KB4470788 was downloaded.

I tried to uninstall this thinking it might be the cause, and of all the updates this is the only one which won't allow me to uninstall it.

So after all that, if anyone's got any ideas as to what's wrong, they would be much appreciated!

Have you tried Safe Mode yet for windows defender? If you can get to it via there not sure if it will update, but at least run a scan with it.