MSSQL 2008 install failed due to SQL Server 2005 Express tools
Faced this problem a little while ago. If you’re searching for a solution, this might help if you haven’t try:
1) Open Run Menu and type regedit.
2) It will open Registry Editor
3) Now go to following location.
HKEY_LOCAL_MACHINE > Software > Microsoft > Microsoft SQL Server > 90
4) Remove/Rename Registry Key 90.
Try again installing the MSSQL 2008, it should resolves the failed state.