I'm a little confused by your statement. Is it black or empty/invisible?
If everything is black, you probably have a mod that changes the player's point of view, most commonly More Player Models does this. If that is the case you will need to disable that feature, for MPM, press F12 to disable point of view.
If it is empty and you're playing on a server, make sure you have the nether enabled in your server.properties. I don't think you can disable the nether on singleplayer, but I could be wrong.
If none of this helped you, please post a screenshot and your Minecraft log.