What is the NetBIOS computer name of your BES? The netbios name must be reflected in the MDS_CS server name.
Read through this:
BlackBerry MDS Connection Service starts and stops unexpectedly
Doc ID : KB11117
Last Modified : 2008-02-26
Document Type : Support
BlackBerry Search Results
And this:
Unable to Start the BlackBerry MDS Connection Service after upgrading to software version 4.1 service pack 2
Doc ID : KB10865
Last Modified : 2007-03-26
Document Type : Support
BlackBerry Search Results