Solver doesn't seem to react
 

I need some help using solver. I've used it many times before so I'm not sure
what I'm doing wrong here.

Simply put, the equation is as follows:

ax + by = z

x and y are percentage so that x + y is always 1 or 100%.

There are MANY ax + by equations and I am looking to minimize the standard
deviation of the entire dataset by defining x and y.

So the standard deviation cell is my target cell, with the target of
minimum. I want to adjust x and y = 1- x so it changes itself. I defined
constrains as x cannot be less than 0 and greater than 1. I asume linear
model and then click solve.

Nothing happens.... What am I doing wrong? Any help would be greatly
appreciated. Thanks so much.....