Can't log in – login screen has changed

I’ve been trying to log in to a client’s site for a week now without any success. I’ve searched through past support docs and I’m not seeing anything that corresponds to what I’m seeing.

I noticed that the regular wp-login.php page has been replaced with a ‘generic’ login screen which pops up – and I’ve got no links for resetting my password.

Any suggestions as to what might have happened here – and more importantly, how can I access the login? The client called this morning and is wondering where the new content is. Thanks in advance.