My 2005 Mini Cooper won't start. I think it's a battery issue, but the battery isn't dead. (The lights will go on, the remote lock works, etc.)

When I try to start it, all the notification lights will go on, and the headlights will go on. When I turn the key to make it turn over, it makes a banging noise and the headlights flash. There is also a beeping noise, but I'm not sure where it's coming from.

Any ideas what this might be?

 

Will it crank over? Any error messages?