The FBI Virus can be tough to fully get rid of.
Formatting and restoring the system is the best way to go.
Not sure of your experience with computers but you could always pull the drive and plug it into another system as a slave drive, then scan it from that system, that will usually get it back up and running to a point where you can scan it with other programs to try and finish cleaning it.
There is still no way to know if its fully clean because there will be multiple program installed.
That's why formatting it will be best way to go.
Just be sure and backup your data first.
Then scan it before you copy back over to the restored system.