I found it:
To view or change the compatibility level of a database
1.After connecting to the appropriate instance of the SQL Server Database Engine, in Object Explorer, click the server name.
2.Expand Databases, and, depending on the database, either select a user database or expand System Databases and select a system database.
3.Right-click the database, and then click Properties.
The Database Properties dialog box opens.
4.In the Select a page pane, click Options.
The current compatibility level is displayed in the Compatibility level list box.
5.To change the compatibility level, select a different option from the list. The choices are SQL Server 2008 (100), SQL Server 2012 (110), or SQL Server 2014 (120).
Great.
SQL Server 2014 doesn't know databases previous than SQL Server 2008 even if they are attaché in a SQL Server 2008 instance. The compability need to be set at 10 at minimum to be recognized by MSSQL 2014.
thanks!