Execute the following Microsoft SQL Server T-SQL administration script using Dynamic Management View(DMV) and Dynamic Management Function(DMF) to list all blocking and blocked queries(sessions):

USE AdventureWorks2008;

GO

SELECT BlockedSPID = blocked.session_id,

       BlockedQuery = blockedsql.TEXT,

       BlockingSPID = blocking.session_id,

       BlockingQuery = blockingsql.TEXT

FROM   sys.dm_exec_requests blocked

       JOIN sys.dm_exec_requests blocking

         ON blocked.blocking_session_id = blocking.session_id

       CROSS APPLY (SELECT *

                    FROM   sys.dm_exec_sql_text(blocked.sql_handle)) blockedsql

       CROSS APPLY (SELECT *

                    FROM   sys.dm_exec_sql_text(blocking.sql_handle)) blockingsql;

GO

Related article:

How to monitor blocking in SQL Server 2005 and in SQL Server 2000