Try running a full scan in safe-mode with the latest definitions. If that fails to detect anything, there are a few other tools that you can try.
1. Norton Power Eraser - http://security.symantec.com/nbrt/npe.asp?lcid=1033&origin=default
Because the Norton Power Eraser uses aggressive methods to detect these threats, there is a risk that it can select some legitimate programs for removal. You should use this tool very carefully, and only after you have exhausted other options.
2. Microsoft Malicious Software Removal Tool - http://www.microsoft.com/security/pc-security/malware-removal.aspx
3. Malwarebytes - http://malwarebytes.org/
In the future, you can visit the Norton Community for Norton related issues.
http://community.norton.com/norton/
Cheers,
Thomas