In some cases, for security, we have put in place restrictions via cached .htaccess to stop malicious entities from overseas accessing wordpress administrators.
These restrictions can usually be quite easily bypassed by disabling them, or manually allowing access based on the IP addresses.
Within a .htaccess, you are able to add the following different lines, to enable unrestricted access to the wp-login.php
allow from all
If you would like to restrict it so only certain IP addresses may be able to use the following
allow from 126.96.36.199
deny from all
Generally, this would be done in the top of the .htaccess in your public_html, once this is done, you should be able to access the wp-login.php files.