Several factors could be at fault: tripped circuit breaker or RCD, a faulty or burnt, isolation switch (likely), internal electrical issue within the shower unit (also quite likely). It's important not to attempt repairs yourself and consult a qualified electrician.
With the assumption being every electric shower we've seen (besides Aqualiser) have been in zone 1 of the bathroom, you would want a qualified electrician undertaking the work, 1) To ensure the safety of the shower where you're bringing mains voltage in close proximity to water and 2) so they can sign off their work and notify building control.
