Using For-Next To Fill Cells

i have attempted may be totally in the wrong direction. I have a worksheet where column A should hold the same value for many Rows of information, but instead only prints once in the first row of that section. The # of rows in each section vary; sort of like this - where ... is a blank cell:

A 1
... 2
... 3
... 4
B 1
... 2
... 3

I would like to write a macro that loops through Column A and replaces empty cells with the most recent value. When i run the following code it puts the value in the blank cell, but fails to loop to the next.