If you’re still encountering the QBDBMgrN not running error after restarting your computer, I can help guide you through a few additional steps. First, ensure that the QuickBooks Database Server Manager is installed and updated. Then, check that the QBDBMgrN service is running by going to the Services app in Windows and starting it if it's not. Lastly, make sure that your firewall or antivirus settings aren't blocking QuickBooks. If these steps don't work, consider reinstalling QuickBooks or contacting support for further assistance.

https://proadvisorsolutions.com/blog/qbdbmgrn-not-running-on-this-computer/