Hi,
First try should be with Power eraser as stated above, if didn't work try with SERT tool.
How To Use the Symantec Endpoint Recovery Tool with the Latest Virus Definitions
http://www.symantec.com/business/support/index?page=content&id=TECH131732&actp=search&viewlocale=en_US&searchid=1301648740176
How to make the Symantec Endpoint Recovery Tool boot from a USB memory stick
http://www.symantec.com/business/support/index?page=content&id=TECH131578&actp=search&viewlocale=en_US&searchid=1301648740176
Security Best Practices for Protecting a Business Environment from Common Threats
http://www.symantec.com/business/support/index?page=content&id=TECH105236