If you mean that you connected another HDTV to the antenna and got the same no signal message then there probably is a problem with the antenna or wire going to it. If it is an amplified antenna make sure it is powered up. If the HDTV did not work with the antenna that the other one did work then try to rescan the channels. Could be that TV has a tuner problem.
Whenever you will notice any problem in signal, in spite of the fact that you have got a new HDTV, consult an antenna installer. Last time, when I noticed problems in signal, I did the same and now I am so happy to watch my favourite shows without any disturbances.