Problem with AD-HOC wifi option

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http://askubuntu.com – I have internet access by ethernet and I want to use my notebook as a wifi point. I want to have internet access on various devices, too. I am trying to make my notebook as wifi access point by using ad-hoc option. I did everything like in this movie http://www.youtube.com/watch?v=gAvnh8TsFEU. I suppose I did everthing ok, according the advices - I checked it a few times. When configuration of ad-hoc network is finished, then my wifi detector going mad. Ubuntu tries to get access to ad-hoc network and it can but only four about 3 seconds. After that there is disconnected. Ubuntu tries to ge (HowTos)