I guess you mean that the image displayed on the LCD screen is upside-down. (It's not likely that the screen is actually upside-down.)
Sp why would this be? Well, when you rotate the screen, the camera flips the image so that it still looks rightside-up to you. This will happen, for example, when you swivel the display out and rotate it into selfie mode. But the point at which the image flips can be pretty close to vertical. So, make sure that your display is completely vertical, i.e. on the click-stop.
If this still doesn't work, then it could be that the sensor inside the hinge which senses the display angle is broken. In that case, your camera will need repair. Whether it's worth it or not on a camera that old is up to you.
