Sadly this sounds like your hard drive is probably on its last legs. That’s not unusual for a device of this age. Folder with a Question mark typically means the Operating system cannot be found. Which is usually caused by a corrupted OS or a failing drive.
It sounds like you mostly want to get data off of this computer? What happens if you try and utilize target idk mode. Press and hold the T key on the keyboard right after you press the power button. Does it go into a different moe? It will likely have a Thunderbolt picture onscreen.