This question already has an answer here:
I found a similar question that was already answered. I followed the steps but I still can't recover the website or get into Magento backend. I followed the steps and changed the secure and unsecure base url back to their original value. I cleared every var/cache and var/session folders as well. I still see this when trying to access the backend site:
The requested URL /index.php/admin was not found on this server.
Help would be VERY much appreciated.