1) I'm not sure if this works with hydra specifically, as an alternative to man -h, -?, and --help are good things to try as well.
2) You should look at the actual login form (view source) and see what method is used there is basically zero reason for it to be HEAD, it "could" be GET, but is likely POST. It could also be basic or digest auth and not use a form at all.
3) Is 'Admin' the actual username? When you say you have to select it from a dropdown do you mean a dropdown implemented by the browser's auto-complete or a dropdown which is actually part of the login webpage? If the later then the value you need to provide to hydra might not actually be "admin", you'll have to understand HTML look at the page source to find the actual value.
4) You could fireup wireshark or ettercap and capture a known good login sequence and then you'd know specifically what's sent back and forth when you login.
5) When you fail to login via the browser are you simply redirect back to the login page or is there an error? Does it generate a 403 forbidden (or similar), give a 200, or one of the redirect response codes?