Troton opal shower completely stopped?

Unlike the others my shower completely refuses to offer any water. Going fine for years but during a recent shower it just stopped completely. Power light is ok but on pressing any button the indicator changes to the cool middle one and then won't move either way until switched off. The low pressure light also comes on.

Could it be that there is a blockage in the feed pipe or maybe something more sinister.

Unfortunately I am unable to locate the operating instructions. Shower is probably about 7 -8 years old.