Why is power reaching my GR-S505 camcorder, but not the on/off switch?

When mains power is provided, this is evidenced by lighting up the viewfinder but clearly not getting further than the control-panel on/off switch.

Having recently used the camcorder to replay and record most of my C-Cassettes into a DVD HDD, this sudden fault forced me to try utilising JVC's excellent 'conversion-to-full-size tape' Adapter, in a well-known up-market manufacturer's VCR.

Sadly it seems the JVC's auto head-cleaning facility is apparently considered unnecessary in the full-size tape playing VCR market, and one seriously mauled C-tape later, I'm now desperately keen to overcome the otherwise so-far perfect camcorder's power-failure.

Can anyone please help?