Symptoms

Once I modified the K2 Service account password in Active Directory, K2 stopped working
 

Diagnoses

Ran K2 in console mode (the customer is on a Dev license), inserted the new password when prompted. Ran the Setup Manager to insert the new Service password into K2. This allowed access to K2 Workspace but not to K2 Designer Runtime. Discovered the customer has multiple domains so added the second domain back into Workspace and verified it was successfully added in the config file. Then discovered other users could not access K2. Updated the Active Directory service instance to reflect the second domain.
 

Resolution

Running the setup manager for both Blackpearl and Smartforms and then adding the second domain back into workspace and into the AD service instance resolved the issue in this Dev environment.

Customer also asked for instructions for how to do this in Prod - the major change will be that the K2 Service password will need to be changed on the K2 Blackpearl Service (right click select properties, change PW). It does not prompt for the password change like console mode does.