Blinking err, no shutter

I found my old D90 and tried to take a few pictures but it doesn’t work.

• Viewfinder is dark
• Live View doesn’t turn on.
• When half-press shutter-release (trigger autofocus) Err starts blinking. Goes away after a while.
• When fill-press shutter-release I hear a motor buzz but nothing else happens, no AF, not shutter, nothing.

What might be the issue? Is it hard to fix?