How do you know the electrical supply is on at the shower? There should be an isolator, usually a large pull switch on the bathroom ceiling or a large wall switch outside. It will usually have a neon indicator.
How old do you think the shower is?
Can you see the Amperage of the supply MCB and the size of the cable?
It sounds rather like it.
I suppose an easy test would be to watch the electric meter going round,
If the element is OK it will be fast if U/S it maybe won`t move.
Or call an electrician to test it properly.
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