EventSentry requires the EventSentry agent to installed on running on all machines that you need to monitor. If the agent is not installed or stopped, no monitoring will occur.
If the EventSentry is stopped, then you can either start it by opening up the "Services" control panel, selecting the "EventSentry" service and starting it, or you can start the service from the management console using the remote update features.
If the service is not installed, then you can install it using the EventSentry management console. Either click the "Remote" menu or right-click a group and/or computer and select "Install & Configure Agent".
If you are upgrading from a trial version, then you should open the EventSentry management console, click the "Remote" menu and select "Update Agent(s)" to install the latest license key and restart the service.