A full reset should fix the problem you are having. Power the keyboard off, then press the Octave + and Octave - buttons at the same time and power up the KeyLab. All of the buttons will flash to indicate the reset was successful.
Before anything, you should try to load a stand-alone virtual synth and try to use your KeyLab there. Make sure the KeyLab MIDI inputs are enabled. If the keyboard works, then you know the problem is specific to Ableton. If you don't have a stand-alone synth to test, then follow the instructions below.
First, you need to determine if Ableton is actually receiving any data from the KeyLab itself. The easiest way to do this is to move the pitch with the KeyLab connected to your computer and Ableton Live running with a blank session. If Ableton is receiving data, you will see a the MIDI indicator located at the top left corner of the program blinking. If the IO button is enabled, you should also see the ALL CHANNELS indicator for the selected track blinking (Assuming the selected track is a MIDI track). If the indicator is not blinking, then you might need to remove and reinstall the KeyLab drivers.
If the indicator blinks, make sure that it will also blink when you play the keys on the keyboard. If the indicator does not blink when you play the keys, then you definitely need to contact support.
If the indicator does blink, then try loading an Instrument Rack and load a patch from the Ableton browser. Make sure the MIDI FROM setting for the track where the Instrument Rack is loaded is set to ALL INS, monitor is set to AUTO, and that the record enable button is red. Play your keyboard, you should hear something come out of your speakers.
If nothing is coming out of your speakers, check the Ableton Preferences, MIDI tab. If the Keylab is listed as a control surface, then remove it from the list. Make sure that the KeyLab input or output port is not assigned to any other control surface on the list. Then under MIDI ports, the Keylab Input port must be enabled for Track, but Sync and Remote should not be selected (for now, at least). Save your changes and close the Preferences window. Try playing some notes. If you still can't hear anything, contact support or take the product back to the store where you purchased it and exchange it for a better product, or if you are a masochist just exchange the KeyLab for another one that is in working order.
Hope this helps.
Also, Arturia does not consider us, the end-users, their customers. Arturia's customers are the Sweetwaters, Guitar Centers, and Sam Ash stores of them world. Don't forget that. That is right! Arturia has told me they do not monitor these forums at all! The admins with 'Arturia' in their name that you see answering posts from time to time are not really Arturia employees, they are paid by Arturia to deal with the pesky end-users like you and I. When you take that into consideration, you begin to understand exactly why there are so many angry end-users on these forums.
End of rant.
