I have the exact same problem. Have used AVG rescue disc which missed this virus and then used Norton Bootable Recovery Tool. This picked up a handful of adware and a trojan, all of which were dealt with but the same problem persists. I cannot boot in safe mode either, which makes installing anything to deal with the specific threat impossible too.
When I get as far as the desktop I can see the files it has renamed (with locked) and know if I get rid of this virus the next stage will be accessing these files.
Although surprised, due to the prevalent varieties of this ransomware, that Norton do not already have an available response in the recovery tool. Thanks for any advice you can offer.
[edit: Clarified subject.]