After migration succeed Sharepoint still trying to access the old Sql. Huge error in event viewer

Hello everybody,

i succeed to do my migration of SQL server of Sharepoint by using NewSql\Instance2 instead ofOldSql\Instance1 . I did this by  the command "stsadm -o addcontentdb -urlhttp://parV0XXX–databasename "WSS_Content_ATP" -databaseserver "NewSql\Instance2"  and "stsadm deletecontentdb "OldSql\Instance1" it suceed.

To be sure i shut down all the database of OldSql\Instance1 and my Sharepoint site worsks withNewSql\Instance2:)

But when i look in the event viewer ive got around 1000 erros saying that my sharepoint still trynig to access OldSql\Instance1 .Its very weird and i think because of that all of my sharepiont site are very slow.

In the log its very this is what i have :

#50071: Unable to connect to the database SharePoint_Config on OldSql\Instance1,1497.  Check the database connection information and make sure that the database server is running. 
08/06/2015 10:13:21.43  OWSTIMER.EXE (0x113C)                    0x05F8 Windows SharePoint Services    Database                      880i High     System.Data.SqlClient.SqlException: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 0 - A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.)     at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)     at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)     at System.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternalConnec... 

What should i do to stop Sharepoint to try to access to OldSql\Instance1? (because this Sql Instance doesn't exist anymore we shut down all database)

Regatrds,Charles