It seems that Dangerous Knowledge was taken down from Google Video. Here is a link to the BBC page:

http://www.bbc.co.uk/bbcfour/documentaries/features/dangerou...

"In this one-off documentary, David Malone looks at four brilliant mathematicians - Georg Cantor, Ludwig Boltzmann, Kurt Godel and Alan Turing - whose genius has profoundly affected us, but which tragically drove them insane and eventually led to them all committing suicide."