1 check water supply if too low or blocked the machine will not start.
2 see if there are any codes numbers showing.
3. Remove the sieve and check under that the pump is not blocked by debris

Hope this helps

8 reasons :
https://www.appliance-insurance.co.uk/appliance-insurance-articles/reasons-dishwasher-beeping/
Dishwashers equipped with an electronic control, which may display blinking lights or have beeping sounds. ... A beeping sound every 30 seconds: Indicates the dishwasher door was unlatched during the cycle. Close the dishwasher door to resume the cycle. https://products.geappliances.com/appliance/gea-support-search-content?contentId=17380