A phone that will not find a network is annoying, and two things cause this most of the time. Both take a minute to check.
The card is in the wrong way round. It goes in with the gold connectors facing upwards and the little cut-out facing away from the phone. Once it is seated, power Ringo off and on again.
The card has not been activated yet. A new SIM often needs activating before it will register on a network. Your provider's instructions will say how, and it is usually one phone call or one text message.
If neither of those changes anything, email us at [email protected] with a photo of the SIM in its slot, and your order number if you still have it, and we will tell you what we can see.