Try these five ways:
1, find the Control Panel -> Uninstall Programs -> Programs and Features, all the programs are uninstalled SQL Server starting with a clean
2, find SQL Server2008 previous installation directory together also permanently delete (trash also clean, delete)
3, clean up the registry and delete traces of antivirus software
4, anti-virus software does not completely removed, into the C drive will delete Microsoft SQL Server folder (Normally there is something can not be deleted, because there are some process to boot straight run directly with file shredder,), the folder there is also the default in the Program files folder to store one instance of a file, if they remember together also deleted
5, delete the registry information into the command prompt run -> regedit dialog box appears
HKTY_CURRENT_USER-> Software-> Microsoft-> Microsoft SQL Server (there may be more, all deleted) HKTY_LOCAL_MACHINE-> SOFTWARE-> Microsoft-> Microsoft SQL Server XXX (there are many, all deleted)