Originally Posted by warmshed

You say the bike's electrical circuits die when pressing the start button. When you release the button do the lights come back on? can you sound the horn?

If so then it would boil down to a bad connection to the starter motor, either earth or live feed, remember it goes via the starter relay which also must be low resistance and functioning correctly.

If the battery does not recover and bring back the lights and horn then it would point to a battery fault.

A faulty starter motor can exceptionally draw too much current or prevent itself working due to internal fault but I would make sure everything else is right first as this is a much lower probability.

My thoughts are that the battery will be the culprit.