Entering Random numbers to a 2D array with no Duplicates

I want to enter 64 different numbers into an 8*8 array but I am having problems...

int[,] check = new int[8, 8];
        Random rnd = new Random();
        int[,] T = new int[8, 8];
        for (int i = 0; i <=7; i++)
        {
            for (int j = 0; j <=7; j++)
            {
                int num = rnd.Next(1, 64);
                check[i, j] = num;
                while (num != check[i,j])
                {
                    T[i, j] = num;

                }
                Console.Write("{0}\t", T[i, j]);
            }
            Console.Write("\n\n");
        }