What is a Windows service, and how would you troubleshoot one that will not start?

A Windows service is a background application managed by the Service Control Manager, often running without an interactive user session. Check its status, configured account, dependencies, startup settings, and service-specific logs. Review Event Viewer for the exact failure and verify required files, ports, permissions, and configuration. A service may fail because its account password changed or an upstream dependency is unavailable. Use supported restart and recovery settings, and avoid repeated restarts before capturing evidence if the failure could corrupt state or obscure the original error.