If you are receiving the "cannot connect to database" error message on the machine/server where the database is held (server), there are a few things that need to be checked before proceeding. 

Firstly, we would always recommend re-starting the machine/server that holds the database and trying to access TaxCalc after a restart. If this works, you may want to check whether the Postgres service is set to delayed as per our article for Postgres does not always start when the "server" machine is rebooted. 

In order for TaxCalc to work, we require two windows services to be started. 

1. You need to check the Postgres service is running. On the server, go to Start > type in Services and click on the option to open this prompt. Locate Postgres 9.4 in the list and check the status. A local administrator should have the option to start/stop/restart this without any errors. If this is already shown as running, please restart the service and ensure this starts and stops as required. 
   If you are prompted with any errors, this is a permissions issue and needs to be taken up with your IT team. TaxCalc are unable to assist you in this instance.
2. If TaxCalc still doesn't work on the server machine once the service is up and running, you need to ensure that your firewall configuration allows the TaxCalc traffic to pass through. 
   1. You can try temporarily disabling your firewall to see if this allows TaxCalc to open. If it does, you will need to amend the rules to allow the ports to be open for TaxCalc and add TaxCalc as a safe executable. For more information on how to do this, please see the articles for How do I configure the firewall for the Network version of TaxCalc? and How do I configure my firewall software?

Usually the above troubleshooting resolves the application not working. If TaxCalc still does not work, are you able to check if there are any other applications that you are also experiencing difficulties with? If so, this may indicate that there are other issues that need to be addressed and we would recommend contacting your IT team accordingly. Please note TaxCalc will not be able to assist you with this. 

If TaxCalc is now operational on the server but you continue to have issues connecting from the client machines please see our article for Cannot connect to DB - Client machine