all discounts have been removed from our website

We have different discount levels on our site from 15% -50% off. Today None of the discounts are showing I have reapplied the rules and flushed the cache but it’s still not working? Our Dev is on holiday until the 4th and we are in full sale mode. It’s saying “One or more indexers are invalid. Make sure your Magento cron job is running.” how do I check the cron job and make it run? any help appreciated.