First thing to check is how NetXMS Core Windows service is doing. NetXMS Core is the server process to which management client connects. Does it appear as "running" in Windows services?
If it's not, you can check it's log, it's typically in C:\NetXMS\log\netxmsd.log (you can check location in C:\NetXMS\etc\netxmsd.conf server configuration file). Log should give some insight in what's happening, may be it's waiting for the database or something.
