Well done for being suspicious, you would be amazed how many users fall for this!
This is a well known Tech Support Scam do not click anything on that page and do not phone any number on that page.
When this happens and your PC seems to be locked, open Task Manager (Ctrl + Shift + Esc)
On the Processes tab, locate your browser in the process list, then right click and end task on the browser process.
You can then continue to user your PC and browse the Internet
This is caused by a browser re-direct on a page you are visiting, try to avoid any page that jumps out to this sort of page.