This kind of virus is called ransomware because your computer is being held for ransom.
But even if you send the $200 as instructed, your computer will not be unlocked. The scammers just walk away with your money.
To get your computer up and running, most likely you will need to take it to a repair shop.
Without a solid idea on how the virus is being spread, it's hard to say what to avoid. But it's important to have the latest anti-virus software installed.
If you have a locked up computer, are very computer savvy and have access to a separate working computer, you can try to remove the virus yourself.

source: here