Yeah it's an obvious scam. Perhaps you should forward their payment information to the real FBI. This sounds like it falls under the category of wire fraud. And also buy a decent antivirus program. It sounds like this scam is being perpetrated by a computer virus attack on your system. ANd change your password after you get this resolved.
It probably wouldn't hurt if YOU contacted the FBI. It's a federal crime to impersonate them.They'll know how to best handle this. Who ever this is, might be using a virus to control your computer. Try a hard reboot and see if it clears. I've seen this scam before.