I was trying to change the isolation level of my database using the ALTER DATABASE statement and the query was running for hours to execute it, because there were ongoing transactions in the db which is preventing the isolation change. I have solved this problem by taking the DB into single user mode before running the alter statement using below script
if(charindex('Microsoft SQL Server 2005',@@version) > 0)
declare @sql varchar(8000)
select @sql = '
ALTER DATABASE ' + DB_NAME() + ' SET SINGLE_USER WITH ROLLBACK IMMEDIATE ;
ALTER DATABASE ' + DB_NAME() + ' SET READ_COMMITTED_SNAPSHOT ON;
ALTER DATABASE ' + DB_NAME() + ' SET MULTI_USER;'
Any changes to Database level properties in SQL Server can be done easily through the use of single user mode, which permits only one connection to be made to the database at any time.