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.
Mike O'Sullivan: Of course, it doesn't mean the aerial isn't the problem. What I've said is simply making you/her aware of what sort of reception location it appears to be. Obviously with deciduous trees the signal might be worse in summer when the leaves are present.
It might be worth asking the landlord if they have any knowledge of the issue.
Are you sure of the post code given? A search shows that to be in Pilpot Wood on the Bowood Estate and between Derry Hill and Sandy Lane. It is therefore near the top of a hill (near rhe Naish Hill local radio mast) and should be able to get good reception from Mendip. But an 8 element aerial is unlikely to be sufficient in that location. Therefore it would be worth having an aerial installer inspect the current system with a view to replacing it with a log-periodic aerial that will suffice for the foreseeable future. Do not fall for the 'scam' of a "Digital Aerial", all UHF aerials are perfectly able to receive Freeview transmissions.
Mike P : Much as I hate to contradict, but to me anyway, that post code indicates a property located at the end of a gated lane that runs off the A342 in one of the worst locations for Freeviewreception from Mendip, insomuch with any aerial nstalled for reception from the aforementioned station having to face in a direction that skirts along the sides of a rather dense forest, that is, if not actually in it!
MikeP: Apologies Mike, I had another look at the view from said p/code location on a somewhat larger screened monitor, and on zooming in on said view can detect what would appear to be the mid/upper section of a mast in the extreme distance, the mast being positioned slightly to the RHS of two others at a shorter distance away.