Services stop / shut down offline with timeout error

Hi guys we have a serious issue in production... thank God it's on our slow period :

The nav serviced, without any explanation, decide to stop. All services work when they are online. User account is a domain account.

The services are on auto-start. The only remote explanation I have is this error in the windows application log, does thta ring a bell to anyone :

Service:
User: BELISLE-LAN\navservice
Type: System.Data.SqlClient.SqlException
Class: 11
LineNumber: 0
Number: -2
Server: NAVTEST
State: 0
Source: .Net SqlClient Data Provider
ErrorCode: -2146232060
Message: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.
StackTrace:
at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
at System.Data.SqlClient.SqlDataReader.ConsumeMetaData()
at System.Data.SqlClient.SqlDataReader.get_MetaData()
at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
at System.Data.SqlClient.SqlCommand.ExecuteReader()
at Microsoft.Dynamics.Nav.Runtime.NavDatabaseChangeListener.TryExecuteReader()
at Microsoft.Dynamics.Nav.Runtime.NavDatabaseChangeListener.CollectTrackingObjects()
at Microsoft.Dynamics.Nav.Runtime.NavDatabaseChangeListener.TimerHandler(Object param)



I've tried shutting down the SQL Server for 1-2 minutes but that does NOT crash the services. However apparently putting a lot of stress on the server like a major file import while renaming a company crashes the service everytime (3 times in a matter of 15 minutes).

Again when the services are online we can process our orders without any problems..