I'm assuming that
| 0 2 |
| 0 0 |
is a coefficient matrix A for some
X = [x y]^T (X is the column vector of variables)
C = [a b] (C is just some column vector of constants)
In that case x does not equal 0. In fact, x is not even in the system of equations since its coefficients are all 0's anyways.
Rewritten in the form of equations, your matrix translates to:
0x + 2y = a
0x + 0y = b
So if b does not equal 0, then there is no solution to the matrix
also y = a/2 for all possible values of a
x can be anything.