Key on, clutch in, crank the starter. If no engine start, don't turn the key off, just open
the throttle a little and crank it again. Just in case it's flooded.
Still no start? Maybe it's starved, turn the key to run the fuel pump, turn it off, turn it on
again before cranking to be sure of enough pressure for a start.
Still no start? Key on, turn the throttle a few times to full open and back to full close to cycle
the ECU throttle response. Key off, key back on and hit the start button.
Still no start? Remove the seat and find the terminal disconnected when replacing the battery.