Just some ideas and I don’t know if any will work or not.
i). Try removing the battery from the camera and then turning the camera on and leaving it on for 20-30 minutes, then turning the camera off, reinserting the battery and turning it on to check.
The idea behind this is that most cameras have a rechargeable back up battery or capacitor mounted on the motherboard which is used to maintain the settings when the camera is off or when the battery is removed for whatever reason. I can’t find where it says in the user manual how long the settings will be maintained for by the backup battery but with other cameras it varies between 1-10+ days. By turning the camera on without the main battery it forces the backup battery (or capacitor) to discharge more quickly. When it has discharged all the settings should default back to their factory default settings.
ii). I’m wondering if only the backlighting in the LCD screen is turned off when the EVF is selected i.e. dark LCD screen and not that there are no images still being sent to the screen.
With the camera on try shining a flashlight at an angle close to the LCD screen and check if you can see anything e.g. menus, images etc. They will be very faint if they are there so trying this in a darkened room may help. If you can see the images then there is a settings reset in the Setup menu (see bottom of p.32 in the user manual). You may be able to step through the menus and reset the camera, using the flashlight to see the screen.
iii). Try updating the firmware. This may be difficult if there are no images seen on the LCD screen with a flashlight although you may be able to step through the menus “blind” by counting the number of steps etc to be able to enable the USB Connection - Mass storage, although it may already be enabled.
Hopefully one of the above will work.