This is the script which I always had in my archive. Following script find out which are the queries running currently on your server.
FROM sys.dm_exec_requests req
CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS sqltext
While running above query if you find any query which is running for long time it can be killed using following command.
Reference : Pinal Dave (http://blog.SQLAuthority.com)