Sorry to hear you are unable to log into your Magento account. The admin login URL is able to be customized during the installation process, so without knowing what your expected admin login URL is, I cannot attempt to duplicate the issue.
Were you able to log into the admin area without a 404 prior to changing the username and password? How did you change that information? Was it in the back office or via the database? What specifically did you change? Have you tried rolling back the changes to see if that helps?
Sorry to hear you are unable to log into your Magento account. The admin login URL is able to be customized during the installation process, so without knowing what your expected admin login URL is, I cannot attempt to duplicate the issue.
Were you able to log into the admin area without a 404 prior to changing the username and password? How did you change that information? Was it in the back office or via the database? What specifically did you change? Have you tried rolling back the changes to see if that helps?
Kindest Regards,
Scott M