I processed a film and it is completely black?

Possible explanation?
the camera I used is a nikon f3 (second hand) and it was the first film I used.
the shutter seems to work well and I used it in fully manual and A priority on a ilford 400 iso (red label).

I guess that maybe the ISO setting is broken and I'll pass by the store where I bought it to ask explanation (and maybe change the camera or have the money back).
any suggestion?

Added (1). Ok
I've had a reflex in my hands for more than two years now
so it is the first time it happened and I don't believe it was because I didn't remove the cap for 36 exposures

I'll check wheter or not the light is passing through

any other idea?

Added (2). Ok
thank you all for your help
eventually the shutter had some troubles and I'll try to understand if it' s possible to fix it
I leave the best answer open
salut

Where were you shooting… What were the lighting conditions like… Had the film expired… Did you take the lens cap off… Open the back, click the shutter release and see if light is coming through…

If you used it manual you have to tell us for how many seconds you held it open and what the light brightness was. 400 is low light film but still it appears you left the exposure for too long. Oops, sorry, did you mean the film was black or the print was black? If the print, then it means the opposite, there was no light exposure to make an image on the film.

I assume you paid attention to the meter? And tried to set correct exposure. If you did then look at the negatives. This may help a bit:

http://www.ephotozine.com/article/assessing-negatives-4682

Possibilites… The meter is broken. You mishandled the film and got it exposed. The shutter's timing is way, way off.

What is the "it" that is black? If it's the negative, then your shots were overexposed. Wrong camera settings are most likely the cause of this. Or perhaps the second shutter curtain was sticking, thereby leaving the shutter open too long. If the print is black, then your shots were underexposed. This could be due to a shutter that is not opening at all. It could also happen if the film was not taken up on the sprocket and stayed in the can the whole time you were shooting.

Sounds as though your film was very overexposed if the negatives came out black. If your negatives came out clear then they were very underexposed. An underexposed negative printed by a machine will result in a black print.

Open the back of the camera and use the film advance lever to set the shutter and then watch the shutter curtains as you release the shutter. Try it at all shutter speeds a few times.

Its also possible that the linkage between the lens and camera body is defective. Regardless of what aperture you set the lens is designed to remain wide-open (at its maximum aperture) and then stop-down to the taking aperture when you release the shutter. So if you set f16 as the taking aperture and the meter tells you to use a 1/60 sec.shutter speed and the lens doesn't stop-down as you release the shutter you'd be shooting at f1.4 or f1.7 or whatever the maximum aperture is.

So if your maximum aperture is f1.4 and the meter says 1/60 sec. At f16 (the taking aperture you set) and the lens doesn't stop down to f16 your negative will be overexposed by 7 stops.

A good CLA just might fix any problems except a damaged shutter.

Whoever suggested you might have forgotten to remove the lens cap has obviously never used a Single Lens Reflex camera since all you'd see in the viewfinder would be black. Its a possibility with a rangefinder camera or a Twin Lens Reflex but impossible with an SLR.

Do you see the frame numbers on the strip?

p.s. If the whole thing is completely black, then the strip was exposed to light.

When you say "black", do you actually mean "Blank". Even if ISO settings, apertures and shutter speeds were incorrect, you'd still likely see some sort of image exposed onto the film. If the film is truly blank, it's probably because the film wasn't properly hooked onto the take up spool and never actually went through the camera to begin with (I know this because I did this once a long time ago). If it was neg film you shot, it would be transparent brown in appearance. If it was slide film you shot, it would in fact be solid black.