/wp-admin gives a blank page

Hi,

I've got this strange thing going on.
I didn't change anything but the /wp-admin gives a blank page.
Even when a regular user tries to login or signup.

Does somebody know why this is happening?
This is the site:
http://regionofinterest.com/

I'm using WPmu 2.9.2 and buddypress 1.2.3