In this TED talk, Stephen Hawking states with great certainty that their is no intelligent alien life within one hundred light years of us. He states that it is either not there or that intelligent life had been there but destroyed themselves. I disagree. While television signals or radio waves are a logical step on the development chart for an intelligent species, I think we would be extremely lucky to receive such a signal in the short time-frame that we have been listening.
For one, it is possible that these signals are sent out only for a short time-frame for an intelligent civilization. Possibly less than one hundred years. They may discover a superior form of communication and may anticipate that others may be watching out there and therefore not want to be found. An advanced civilization may find a way to mask its signature.
Of course, that's also assuming that life evolved in a way that is similar to ours. The questions is not whether there is intelligent alien life within a hundred light years, but whether there is intelligent life at a similar evolutionary stage as ours with a similar overall evolution. (These items are discussed in more depth on the comments section for the talk).
As a side note, I agree that it is high time that colonize space and yes, I understand that the thrust of Hawking's talk.