So, to undestand this right, there are cracks in the image that is shown and half is black.
It might be just screen or it might be screen and hardware. If image is showing then it's likely that the part apart from the screen is working.
The options you have (to the best of my knowledge) are
1) Buy a screen online (available at various places like eBay) and repair yourself. Risky.
2) Get it repaired by a company like iFix It.
3) Get it repaired by a brick and mortar repair company. There's supposed to be one called 'You Break It We Fix It'.
Even other electronics stores might handle repairs.
4) Get a replace ment Nook HD instead of the Nook Tablet the next time there is a sale. OR ask someone in a store if they'll give you a discount since you dropped and broke your Nook Tablet. If you get a Nook HD for $150 it might be better than paying $80 to $100 for getting the existing tablet repaired.