Backup Exec server failed to start

I have installed Symantec Backup Exec 2012 small business edition running on Windows 2008 R2 Enterprise edition. It was running fine all along and today morning i found an unusual message "QUERY FAILED" in storage tab which was kept on Backup Status(current media) to see the backup status.
I tried to come to the storage tab to see whether the cartridge is online,but it shows the message "QUERY FAILED". So I restarted the Backup exec service which failed to start and recorded the following message.

 An exception occured starting remoting services for Backup Exec Management Service: System.ServiceModel.AddressAlreadyInUseException: There is already a listener on IP endpoint [::]:50104. Make sure that you are not trying to use this endpoint multiple times in your application and that there are no other applications listening on this endpoint. ---> System.Net.Sockets.SocketException: Only one usage of each socket address (protocol/network address/port) is normally permitted at System.Net.Sockets.Socket.DoBind(EndPoint endPointSnapshot, SocketAddress socketAddress) at System.Net.Sockets.Socket.Bind(EndPoint localEP) at System.ServiceModel.Channels.SocketConnectionListener.Listen() --- End of inner exception stack trace --- at BackupExec.Management.Server.RemotingManager.ActivateHosts() at BackupExec.Management.Server.ServerCommon.Start()

I stopped all the services and restarted , but when it started It was asking for username and password when entered says the credential/username is invalid, check whether backup exec server is running. So far I haven't entered passowrd after restarting BE servvices. This is the first time this screen pops up. SQL server is running, port 50104 shows LISTENING and doesn't have ESTABLISHED status; it has so many TIME_WAIT.Nothing has been changed in the server. The backup exec server is running locally and backing up to tape which is connected to the server.