Some times Magento developers faced the issue of below : You are not able to open even admin page and not even able to see any sort of errors on then page. So to solve this type of issues just follow below steps : https://stackoverflow.com/questions/8102777/service-temporarily-unavailable-magento/8275318#8275318
If you try to delete orders in the backend, you will find out that you can only set the status to “cancelled” and the order is still there. Unfortunately, Magento doesn’t allow us to delete those via administration, so you will not find any “Delete order” button. This can be quite frustrating both to developers and the merchants.