C# Random Shuffle Game

I'm relatively new to C#, and am currently working on a shuffle game. The idea is that the numbers are shuffled when the user presses 'new game', and the user then has to get the tiles in descending order by swapping the empty block with any adjacent number.

The swapping of numbers works, but I can't manage to create a random shuffle without having either duplicate numbers or having a '0'.

Help?!