C#: Output first char of a random number 1-10 from an array

I can't figure out how to get my hint button to work by giving the user a hint of the first letter from the array that generates a number from 1 - 10 at Random(); in a french language and output the hint in a MessageBox(); I've already to play a little, but nothing seems to work...

Can someone please help?

http://ift.tt/1MNWggi