What is Cron? It keeps on telling me that it's not running
See here: https://en.wikipedia.org/wiki/Cron

It's probably not that it's stopping - but that it was never set up.  CiviCRM won't do any tasks that need to happen automatically - including sending mails, updating membership statuses, etc. - until you set up cron.  I don't think any of the CMSes that support CiviCRM work reliably without setting up cron, either.

I can't explain how to set up cron for CiviCRM without knowing a lot more about your environment - your CMS version and your hosting environment.  If you're using CPanel or a similar control panel for your hosting, there will be a way to set up cron from within the control panel.  There's some instructions on this page that are specific to CiviCRM.