Shutter blocked, unresponsive commands, turning off by itself

I recently bought this camera used it was quite dusty and the SD release didn't work but sensor and shutter were immaculate and the camera was working fine (I only used with vintage manual lenses and I don't own any Olympus electronic lens to test), then one day I inserted the battery, powered it on and it showed the ART section on screen but was unresponsive to any command, the shutter is blocked in closed position and after a few second it shut down. So I already carried a few tests without lenses and SD cards to see if I could fix it without disassembling the camera.

Test 1:

• Camera OFF, no battery inserted, Left Dial on ART mode
• Inserted battery and turned ON
• ART menu showing on screen, unresponsive to my inputs, Shutter in closed position

I repeated the same Test with every mode and I had the same behaviour with SCN mode, in AUTO mode it showed the focus rectangle, in the other modes the screen remains blank; always unresponsive to inputs.

Test 2 (hard reset):

• Camera OFF, Removed battery
• Power switch to ON position, pressed shutter 30s to discharge any capacitor
• Power switch to OFF position, left the camera in this state for about 30 minutes
• Inserted battery
• Turned ON while pressing Menu+ok simultaneously
• RED LED blinking 2 times while the screen turns on
• Same behaviour as Test 1

I also tried to move the shutter curtain both with camera ON and OFF, it's loose but returns to closed position.

UPDATE 1: I carried another test

Test 3:

• Camera OFF, Battery inserted, Keeping the shutter curtain open manually
• Camera ON, works normally
• I leave the shutter curtain free to move
• The shutter closes
• Camera shuts down

My suggestion is that the shutter mechanism is faulty and causes the rest of the camera misbehaviour

UPDATE 2:

While keeping the shutter curtain open manually I entered the hidden menu, in page 4 are displayed these error codes: 8904 8809 8806 8903 8809