I messed up my installation

Hi guys,
I’ve had WordPress up and running for quite some time now. But yesterday I changed a setting for the “blog” page I think and now I cannot even logon and the site is showing up without a theme.
It’s at https://www.0gravity.co.uk – does anyone know how I can try and logon at all? I am completely baffled here?!
Cheers,
Alistair.