A question in my textbook says - 
A block of mass $m$ is released from rest onto an ideal non deformed spring from a negligible height. Neglecting air resistance, find compression $x$ of the spring. 
I tried using two approaches for this Q but I can't figure out which one if right or if both are wrong. 

1st - 

Using Hooke's Law. 
$$ mg -kx = 0 $$
$$ x = (mg) / k $$

2nd - 
Using Work-Energy theorem. Considering the Gravitational potential energy at the lowest point of the compression to be 0 and since change in KE is 0. 

$$ mgx -(kx^2)/2 = 0 $$
$$ mgx = (kx^2)/2 $$ 
$$ x = (2mg)/k $$

Is any of my approach correct? If yes then why is the other one wrong? Or are both completely wrong?