Windows 10: Need help clearing a lock on my laptop caused by supposed trojan horse

I got a security alert with audio saying my computer was infected with a trojan horse. I am sure the 800 number it gave is not from Microsoft. Can anyone tell me how to clear the lock. Every time I turn the computer off and restart, as soon as I log in the lock screen and audio comes back. I cannot get to my security scan app.Thanks

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Trojan horse

Thanks for information, I am running windows defender offline to see if that can remove Trojan horse

 

Trojan Horse warning from Microsoft?

Received message that, due to a Trojan Horse, my computer was locked. Against their warning, I turned off computer and didn't find a warning in Microsoft Security. Is this a scam, or from Microsoft as claimed?

 

Trojan Horse

Is csrss.exe a trojan horse? It seems to me. it's part of system 32. It was installed on my computer in August 2013 by Microsoft. Need to know as soon as possible. I've been harassed by outside vendor to buy a very expensive firewall.