Are you sure the battery is good ?

The mirror requires battery power to flip down as well as flip up. If the battery did not have enough power to flip it down again it would stop mid cycle and that causes a big problem as it will not reset itself.  This is the reason they tell you to use the mains adapter when using mirror lock up. 

Touching the mirror is likely to cause a focusing problem and the focus will need to be reset by Nikon unless you are very brave.  Check your focus with the longest telephoto you have if the image in the viewfinder is sharp but out of focus in the saved image it needs servicing. The problem will affect AF and manual focusing.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html