If you add a new/demote/change a domain controller
We had major problems and service desk support did not provide much help. We installed a new domain controller and demoted our original one to a member server. About 12 hours after doing this we found that no one could login to Service Desk. After much investigation we have found the solution ourselves. In the SQL Service Desk database there is a table called ActiveDirectoryInfo, you need to amend the servername to the new domain controller!!