The QuickBooks Connection Diagnostic Tool can resolve company file and network problems in QuickBooks. To access it, download the tool first from the Intuit official website. After installation, launch the tool and navigate to your company file. It will check for issues involving the setup of the network, firewall, or database connection. If there's a problem, the tool will attempt to resolve it automatically. This tool is quite useful when QuickBooks is unable to connect in multi-user mode. Once the scan is finished, reboot your computer and attempt to open your company file once again. The QuickBooks Connection Diagnostic Tool saves time and gets QuickBooks up and running without the need for expert assistance.