I lost usb communication during downloading (20160822_s12v55_jk_3m ) from SP_Flash to my phone (BV6000). I tried to re-download through SP_flash but now nothing happens. The phone is not switching on anymore.

what can be done to get phone to switch on again?

You may not update successfully, please follow the steps:
enter into setting--about phone--wireless updating--search for the latest version.

windows 10 64? you must install the drivers to recognize the phone

I think flash tool is the only way to repair a bricked device.