You have a pair of Trojans on your computer: Citadel & Reveton. These two malicious programs work in tandem to try to get you to pay them to 'unlock' your computer. We in the internet security biz know this as the "FBI Virus".
You need to take your computer in and have a tech clean it. Those two Trojans are *nasty* to get rid of. I'd back up as much of your info as you can, and take the computer in to a tech.
Sorry I can't give you better news. You *never*, NEVER want to send money using green-dot or a pre-paid card to an unknown person or company.
It's a SCAM.
"Tempus veritas revelat.
" - Time reveals truth.
"It's the mythology of a sun god who wished he was a man because he saw something so great in us.
It's the story of a hero who could move whole worlds and see through stars and hear a whisper on the other
side of the planet...and who fell in love with a storyteller." - ashmaht (x)