white page after update

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after a view year not doing much with my concrete5-webpage i found out today that - for example - the captcha in my contact form didn't appear. Before thinking about any reason I thought it maybe could be time to update c5.
I created a backup via dashboard, and updated - again via dashboard. I got a successful-message after a view seconds and switch to my page and there's only a white windows without anything, same if I try to go to the dashboard - white...
So I don't have the chance to undo this update or to restore...
any ideas?
my page would behttp://www.bwsc.at

thanx a lot!