login - wp-admin seems to be redirecting in WordPress

The main cause I've seen for this is incompatible plugins. Via FTP, either download and delete all your plugins, or rename the existing plugins folder to plugins-old (or whatever) and make a new plugins folder.

After this, copy your plugins from the old folder to the new folder one by one until the problem reappears. At that point, you have your culprit. Look for an updated version (after deleting the offending plugin from the new plugins folder so you can log in) of the offending plugin and go from there.