Plug the TV aerial cable directly in to it and from there to the TV. Now run the setup menu and get it scanning for channels If it doesn't find any then take it back to Argos (Mikomi is an Argos Own Brand.) for a full refund.
It doesn't matter about the receipt. As Mikomi is an Argos Own Brand it MUST have come from them.
Additionally, under the Sale of Goods and Services Act, during the first six months it is up to Argos to prove that it isn't faulty rather than you prove that it is.
t
February 2008