I tried to upgrade SQL Express 2005 to SQL Express 2008 but it failed while trying to stop/Start a system service. I stopped the service manually and uninstalled all SQL Entries from Add/remove programs. I tried re-installation but it wouldn't install before because of an error : Error code 0x84B30002.
I again removed every SQL 2008 program from Add/remove and also deleted the 100 and MSSQLServer10 folder from Program files\SQl server.
Now receiving this error message :
[Error Message] The instance ID 'MSSQL10.MSSQLSERVER' is already in use. Please choose a different value.
[Details] Microsoft.SqlServer.Chainer.Infrastructure.InputSettingValidationException: The instance ID 'MSSQL10.MSSQLSERVER' is already in use. Please choose a different value.