Hello there,
I am Jaspreet Singh.
Please ignore the message and instead press ctrl+shift+esc keys together.
Check the list for any app that is running which is not installed by you or seems suspicious (if you are unsure post a picture of the taskmanager here with the running processes tab open) Once done you should have control of your system.
Go to settings/apps/installed apps and look for an app that you did not install and uninstall it.
Do the same for controlpanel/uninstall a program (search for control panel in the search box on taskbar and press enter to open it)
Apart from these look for installed extensions in your browsers and similarly remove any extensions that you do not recognize.
** Your system is not actually infected with trojan or any such, there is simply an app or extension installed on your system that shows the popup and terrifies you to call the number so that the person behind this can sell you a care plan.