phpMyAdmin won't let me login - no error shown

My issue was, I was using HTTP instead of HTTPS. I don't know why, my server allows both connections, but I must have made a change some where so it only allows HTTPS connections. Once I switched over, the website started to work again.

In my case, the hard drive on the server was full.

In Linux, use df -h to view the available space on the hard drive and clean up unnecessary files.

I just spend forever troubleshooting this.

You are missing the mcrypt extension.

The mcrypt extension is missing. Please check your PHP configuration

You can check if this is the case by forcing

$cfg['Servers'][$i]['auth_type'] = 'http';

and looking at errors when you login.