It sounds like, although all you see is a small crack, more damage has occurred. Since you can see the screen and it lights up, I would hazard a guess that it is not completely connected in side. As in, something has come loose. Also, the damage could be enough that the display has to actually be replaced. Unfortunately the only way to know for sure is to open it up and take a look inside.
Now if your tablet is still under warranty, you don't want to be messing with it in that way. It would then be better to contact they manufacturer.
If it isn't under warranty any longer, and you feel comfortable doing the work yourself, there are many instructional videos online on how to open different tablets and fix potential problems. You can also find the parts online to do a replacement, if need be. Or you could take it to a local tech or repair shop and have them do it.