What is the ROC for this discrete signal: $$ x(k)=4[u(k-2)-u(k)*δ(k-3)]$$

I found that the $\mathcal{Z}$ transform of the signal is $X(z)=4/(z^2)$. 

What would the ROC be?
HINT:

Remember that the ROC is the region in the $z$-plane for which the series

$$X(z)=\sum_{n=-\infty}^{\infty}x[n]z^{-n}\tag{1}$$

converges. Since you've found $X(z)$ you also know that $x[n]=4\delta[n-2]$, i.e. there's only one value of $n$ for which $x[n]$ is not equal to zero. What does that mean for the convergence of $(1)$?