Unfortunately, "live" is technically not really possible as this would require constant connections around the clock and would produce a lot of bandwidth. So PRTG basically monitors in intervals (every 60s, 5 minutes..). When one of these intervals fails (due to an error or due to exceeding a threshold), then you will get notified. So to monitor a service you can use the WMI Service Sensor for Windows and the following guide under Linux by using NET-SNMP.
Monitoring blocked USB ports however might not be possible, at least there is no dedicated sensor for this scenario.