Camera film door will not latch. The door latch

Turn the aperture ring on the lens to its smallest setting (largest f/number). You can control the aperture from the camera body, the same way as with a lens without an aperture ring.

You may download a copy of the manual from here. The film loading instructions begin on page 13.

The sensor on the D80 is smaller than a piece of 35mm film. This means the camera will only use the center portion of the image cast by the lens. This reduces the angle of view, effectively increasing the focal length. The 35-70mm will give you an angle of view similar to a 52-105mm lens on a film camera. Likewise the 70-210mm lens will give you an angle of view similar to a 105-315mm lens.

When you say it was difficult to load film, how was it difficult?

One of the most common mistakes I see people make when they say it was difficult, is they unwittingly shove their finger right through the shutter curtain when trying to load a roll. Since the roll is likely no good at this point anyway, rewind it and open the camera.

Look at the center where you should see what looks like 4--5 horizontal little blades of foil. If these aren't nice and straight, but are crinkled, crumpled, aren't closed, half stuck open, the mirror is stuck open, or any number of other issues - you're toast.

Either consult a qualified repair tech locally if there is one or try somewhere like KEH Camera, you can find them online. If you don't want to repair it, stick it on ebay listing the damage and make $1-2

download users guide from:
http://www.lensinc.net/manuals/Nikon_N6006L.pdf

You can't take the door off. Not without disassembling the camera.
Some system cameras has a small spring-supported pin that holds the door. This is to make room for stuff like film magazines as shown here:
http://www.mir.com.my/rb/photography/hardwares/classics/nikonf2/motordrives/images/NikonF2_MD250_a.jpeg

Nikon doesn't supply the film door any more. You can buy a repair kit from USCamera.com to replace the latch on the film door

Yes, the film door was always a problem on these. The entire door was usually replace since it was one piece with the latch.

I do not believe that Nikon supplies the part any more. You can check eBay for a dead camera, or possibly a new /used door.

The other option is a repair kit available from USCamera.com

There is a safety switch to prevent accidental operation.  Hold the camera like you are taking a photo.  Rotate the camera down so the lense is pointing towards the floor and you are now looking at the bottom of the camera.  On the right is a small button.  In the middle is a slide switch with an arrow pointing to the left.  You need to hold in the button on the right while sliding the switch to the left.

You have to replace the whole door. There is one on eBay, but you won't like the price. Find it here: eBay