How can I fix my Neptune solo shower?

"The electric has gone "

Those four words suggest you don't have any real competence dealing with electricity, expecially a high power device and one that is in a bathroom.

If it is not something simple like the breaker or MCB havindg tripped (And even then you would have to work out whay that had happened) I would strongly advise you to get a qualified techie to look at it. The alternative could involve death. Yours or someone important

XXX
March 2016