I'd think the state of the battery would be the first starting point ... on my old thing it's under the bonnet ... on later cars it's under the panel behind the seat near the rear axle. After that try earthing points.
Try putting the headlights on .... if they're dim the battery is probably flat .... if they're bright do they dim when the starter is tried ... if so then the battery should be suspected again ... if not possibly a solenoid/starter fault.
K
