You’ve got a ransomware and all your files are encrypted. First, search for a decryptor.
If there is no decryptor available, reinstall Windows, and, if you had backups, restore your files.
If there is an decryptor, first of all, run some second-opinion scans, like Malwarebytes, ESET Online Scanner and HitmanPro(because there could be remnants of the virus which can encrypt the decryptor too), and then run the decryptor.
Thanks to the Courtesy of :