Sounds like one of two things, both not good:
1. Is that it is a
scam and you download either a virus or trojan. Have your virus cleaner
do a deep scan and see if you can find anything and delete it. Ensure
that your virus scanner is up-to-date.
2. You are a victim of
“data-hostage”. What that is , is a trojan has been inserted onto your
system, and, if you do not pay a fee, basically extortion, those that
control the program will send a command and encrypt your entire hard
drive and you will not be able to access anything. This normally
happens to big businesses, so the feds get involved.
Hope for your sake that it is the first option.