Dropped and now all exposures are black. - Nikon D3100 Digital Camera

I suggest that you start by contacting Nikon support at www.nikon.com to discuss the problem with them.

Then I suggest that you contact an authorized Nikon repair center for an estimate on the cost of repairs. Some repair centers charge a flat rate which covers any repairable damage including replacement of the camera circuit board.

The last time I had a camera repaired (an Olympus) it cost me a flat rate fee of $150. That was about three years ago.

While the Nikon 3100 is not Nikon's most expensive model, it's still worth checking out and getting repair estimates. The only cost for the inquiry is time.

Also, remember that you will have to pay postage to ship the camera to the repair center though most of them will pay the shipping to return it to you. Ship only the camera body...no lenses, cords, cards, etc. Good luck.

Oops. that hurts. But I'm afraid it won't be worth repairing this one. I already saw the body been sold for less than 300 euro new. And I think the repair centre will ask more for opening and closing this one. Then you still have a used body.
Start saving or perhaps you have an insurance that will pay a new one for you?