Trojan:W32/Reveton is a ransomware application. It fraudulently claims to be from a legitimate law enforcement authority and prevents users from accessing their infected machine, demanding that a 'fine' must be paid to restore normal access.
CAUTION Manual removal is a risky process; it is recommended only for advanced users. Otherwise, please seek professional technical assistance.
Image 1 and 2: Enter 'Safe Mode'.
Image 3: Find and delete ctfmon.lnk from the Startup folder (click image to enlarge).
For more information, see Removing 'Police-themed' Ransomware.