If your are using your qwerty keyboard (an external device) to play the pads on Impact Xt, then goto the track header and select qwerty keyboard under the instrument input pull down menu. Press caps lock to open it.
Turn on the record button on the track header and the monitor button will turn on.
Then turn on the record button on the record panel at the bottom of the song page.
Note; you cannot record MIDI data using a VST virtual keyboard or pads, using your mouse