It a very much a guess at the moment. And there could be loads of guessing. It would be good if you could describe the situation with your device a bit more.
Here are some examples things which would help someone to suggest something useful:
Is it a Satellite Humax device or terrestrial Humax device?
Which Humax model is your device?
Which channel is your strength/quality reading from?
Is it the same for all channels you have tried so far?
What do you mean by “can’t watch”? E.g. Do get a picture but it breaks up?
Is this a unit you have just started using?
Has this device worked before on your current setup? If it is then are you aware of any changes to your setup?
Do you have any other receivers that you could, and have, checked the signal?