When launching Sentinel Visualizer, its splash screen appears, the program loads (you can see the program frame and main menu), then immediately closes.
Sentinel Visualizer is trying to load the last database you opened and its Microsoft SQL Server host is not running.
Open Windows Control Panel
Run Administrative Tools
Double-click on Services:
Scroll down to (and highlight) "SQL Server (SENT4EXPRESS)".
It may show Startup Type as Manual, or be temporarily stopped. Right-click and choose Start:
Restart Sentinel Visualizer
If in Step 4, SQL Server's status was already "Running" the problem lies elsewhere. Email our support team at firstname.lastname@example.org with the issue and we will reply as soon as possible.