I do see the axis, it is however very close in color to the background. If you are using the 9.0 initial release i think the axis is hidden depending on the plotarea background style, anything besides "frame" will suppress the axis. In 9.0 SR1this was changed so that the axis is always drawn as long as its width is greater than 0.
To view the y axis line, go to Properties. Under the heading Expression axes, there is an option called Width. Increase the width to 1pt. This will provide the line for the axes. In case you want to do it for the x axis, increase the width found under Dimension axes.