The FBI/Moneypack and newer ICE CyberCrime ransomware will frequently prevent using System Restore and sometimes using "Safe Mode with Networking" as well.. We've found some success in getting around the "lock screen" by starting System Restore from "Safe Mode with Command Prompt". Try restarting the computer, immediately start pressing the F8 key, once per second till a select screen loads. Use the up/down keys to select "Safe Mode with Command Prompt" and press the "Enter" key.
The next step may require you to be quick. (The malware will try to block this screen as well but it takes a little longer in the command prompt.) Log in as your normal username, and when the command prompt window loads, immediately type: "C:\windows\system32\restore\rstrui.exe", then press the "Enter" key.. When the System Restore window shows up, select a date prior to when the problem happened, click "Next", then follow the prompts to restart the computer and restore back to a time.
After the computer is restarted, if the lock screen is gone and you can access your computer, then download, install, update, and run BOTH of the free tools below, at separate times, of course.. Run full system scans and delete anything they find.
Hope this helps.