404 pages on magento admin and subpages

Question

I am working on a Magento page then after a while I couldn't access my admin anymore

Not Found
The requested URL /magento/chkbackoffice_admin was not found on this server.

also other subpages except for the homepage are inaccessible as well. The site's location is on my VirtualBox's TurnkeyLinux.

I have already restarted the appliance but still same error. Also copied the original directory of the codebase to replace the current site but same error persists. What should I do? Thanks in advance.