To reconfigure the ODBC connection:
  1. Connect to the vCenter Server Appliance through SSH as the root user. The default password is vmware.Note: To enable SSH on the vCenter Server Appliance 5.x, see the Enable or Disable SSH Administrator Login on the VMware vCenter Server Appliance section in the vCenter Server and Host Management Guide.
  2. Run this command to stop the vpxd service:
    service vmware-vpxd stop
  3. Run this command:
    /usr/sbin/vpxd_odbcconfig

    You see output similar to:

    VMware vCenter Server Appliance ODBC Configuration
    
    Choose a database to use with VMware vCenter Server
    
    1) oracle
    2) embedded
  4. Enter 2.You see output similar to:
    Configuring ODBC for embedded
    Operation was successful.
    Database already populated with version VirtualCenter Database 5.0
    Reinitialize database? (WARNING: WILL DELETE ALL RECORDS) [y(es)|N(O)]: OK, preserving the database. (select No to preserve the database)
    Restart vCenter Server now to activate the database changes [y/N]:y
    Successfully restarted vCenter Server

 

Source: VMware KB: Cannot connect to the VMware vCenter Server Appliance 5.x