Not a lot to go on!
I suggest you open MainStage and create a new concert using the "Keyboard Minimalist" template. Go into "Layout" mode and set the keyboard to 88 keys, select "Learn" and press the bottom key on the actual keyboard. That ought to set it correctly. If the "Learn" control remains red, there is nothing coming from the keyboard, if it goes black then all should be well. Go to "Perform" mode and test it. If it is still missing notes, I suggest you use MIDI Monitor (download free from Snoize.com) and check that the keyboard is actually outputting notes across its full range. Please let us know the results of this.