System Cron not working
Use the log viewer extension (you can install it from the extensions tab if the permissions are setup right, or see here: https://civicrm.org/extensions/civicrm-log-viewer).

It should show you what the error is and point you to what needs fixing.

The fact that it went for the 1.5 seconds suggests it's an issue with a specific one of your jobs, so you could go to your list of system jobs (Administer -> System Settings -> Scheduled Jobs) and review the logs of those that are running. Looking at the dates of when they were last run might provide some other clues. You can also manually run them to see if that provides additional clues.

If you're lucky, perhaps you just have a job enabled that shouldn't be enabled.

If you're not lucky, you might have a system configuration problem (e.g. php version, or required php module missing, etc.).