If you are getting the message "no signal" this would indicate that there is a problem with the signal from your dish into your box. Even without a card inserted into a SkyDigibox, if there is a signal, you will always get Sky Guide and the free channels.
Try powering off your box, remove the card, check carefully the cables, especially the connection to the dish, reapply the power and then when asked to insert your card you should then be able to see (for example) channel/SNWS">Sky News on 501 and the BBC News channel on 503.
Once you can see any channel, reinsert your card. This should, after about one minute, give you the channels you expect, such as 103, 104 and 105.
If you continue to get "No signal", you dish may have been misaligned, or there may be a fault with the cables and connectors, or a problem with the Digibox. You can see the signal strength by pressing SERVICES, then 4-SYSTEM SETUP and 6-SIGNAL STRENGTH.