How to delete Petya Ransomware with symantec?

Hello. I have a question about my problem and I do not know if Symantec can help me. Wenn I start my PC I receive the notification from Petya Ransomware: you became a victim of the Petya Ransomware. My desktop is blocked and I can not open any files on my PC. I found an article on: http://nabzsoftware.com/types-of-threats/petya-ran... , they write it happens if someone open unknown emails. But I did not open any unknown emails. How can I delete it now? What symantec tool can help me?