Make sure you have the exact URL you used to setup. If your page cannot be found, I’m guessing it doesn’t exist- meaning you did not type the right URL.
Try checking your hosting settings – Usually you cn find out which url you used.
You may try the following,
http://www.yourdomainname.com/wp-admin
yourdomainname.com/wp-admin
http.www.yourdomainname.com/wp-admin
yourdomainname.com/wp-login
http://www.yourdomainname.com/wp-admin.php
subdomain.yourdomainname.com/wp-admin
yourdomainname/subdir.com/wp-admin.
The first two usually gets the job done. Good luck. I’m having an issue of my own with my wp admin.