This has been going on for a while, but lately, local incidents of this seems to be happening more often, so here is a reminder. If your computer displays an "error" message, or alert, and asks you to call a phone number for assistance, DO NOT CALL THE NUMBER. These are scams that will lead to people that will attempt to charge you large amounts of money to "fix" your problem. Most often, they will want to take remote control of your computer to "fix" your problem. If you allow this, they could have access to any personal information on your system, including credit card numbers, passwords, etc.
The same advice goes for any message claiming to have detected "illegal activity" and asking you to call a number to speak to the police or the "FBI"
If you get one of these messages on your screen, and cannot click on anything to close the message, try holding the power button in on your computer for 10-15 seconds and it should turn off. Wait 30 seconds or so after it shuts off, then try turning it back on, and hopefully it will boot up and work normally.