My Metronic Digi Scart now shows a 'No signal' message. Why?

I have a Metronic Digi Scart. One month out of Warranty it has stopped working and only shows a 'No signal' message. I have tried another digi box on the aerial connection and it works ok, so it is not the aerial connection. Do you know how to open up the box so that I can see if there is a bad connection inside? I cannot find anyway in.

Thank you.