I did a search for this problem and I'm not finding a solution.  I just upgraded to Sonar Platinum from X3, and my new project does not have the "piano" in the piano roll.  Usually, on the left side of the piano roll there are white and black "key"S that look like a piano.  You can use these keys to reference where you are on the grid and also to trigger that note.  However, in Platinum, when I open a piano roll view of my midi track, there is no "piano" on the left side....there's nothing, not even a small window pane there (sometimes the "piano" is a list of numbers or instrument names, but in this case their is nothing there at all).
 
Thanks in advance for your help!

Hmmm.... I've got the keys on mine. There's a tab in the upper left corner for enabling different options. Don't remember what options though. Did you try messing with that?

Left click and drag it out. There appears to be a bug of some sort that "snaps" the key/pitch pane shut. 

Thanks for the tip!  Dragging it opened worked! :D

No worries. I'm not sure why that happens but it does from time to time. One of those apparently random bugs.