Nikon D70 photos coming out incredibly dark?

I got a Nikon D70 with multiple lenses from my uncle. Whenever I take photos, they come out super dark. I've tried editing them, but they're so dark that trying to lighten them makes them look grainy, and there's barely any contrast. I've tried multiple lenses, so I know it's not the lens. I've put everything on automatic and even "reset" the camera to factory settings, so it's not the ISO settings. I don't know what's wrong! This is the only camera I/my family has, and I'm going to Turkey next month. I've brought it to some local camera shops, but they say that no one will locally fix a digital camera. I don't know what to do! Has anyone else had this problem? How long would it take if I sent it to Nikon, because I want it in time for my school trip… Does anyone know what I should do?

Dark means gross underexposure.

You need to learn how to use the cameras light meter.

I doubt that you will be able to use your camera effectively in such a short time

Spend as much time as you can spare with the cameras manual in one hand and the camera in the other until you can make adjustments without too much thought

Here are two links that can help

http://camerasim.com/camera-simulator/

http://camerasim.com/slr-camera-explained/

Is it completly dark or just dark in the shades and bright if there's light?

try to shoot in M mode put it on f/22(largest), 2 sec, and ISO 3200and take it outside, the picture should come out completly bright, if not then i guess that the shutter curtain is broken