I want to create an adhoc network. But everytime I click on New adhoc network, it does nothing. Do you know where could be the problem? thanks

Which NetworkManager version do you use? The <hidden network> item in Plasma NM is to connect to an existing ad-hoc network, not to create one.

To create one you go to "Manage Connections" -> wireless tab -> Add -> Wireless (this step is only for recent Plasma NM version). Then you change the "Mode" to "Ad-hoc", type the "SSID" and click "Ok".

If you want the connection to be encrypted then you need to go to the "Wireless Security" tab, choose "WEP" as encryption method (this is the only encryption method NetworkManager supports in ad-hoc mode), type the hex key or passphrase (select passphrase in "Key type" combobox).

Ok, I thought that create network is also for adhoc. Now everything is ok, thanks.