First check silly things like , kill switch? neutral gear?
Is the ignition light on? if not check the battery. next check fuses , (trace the route of the electricty from + terminal) . if the light is on it is a problem with the starter circuit, you can run a wire to the starter relay, if it works the problem is with the button or the brake safety switch you mention. If not, the starter or relay is faulty.
Next time you ask a question give the make/model of the machine. Also say what checks you have already done, so that everyone knows what your level of experience is.
Good luck
Jmmy
April 2009