Lets back up and start with making sure the battery is actually good. Need to have it load tested to check output. And that doesn't mean with a volt meter because you can have 12.7 volts with a meter and drop to 0 under load. A clicking sound could also be a safety switch or even the fuel solenoid on the bottom of the carb, or possibly the pto clutch if somebody forgot to disengage the deck.
Also make sure you can turn the flywheel by hand to make sure the engine isn't locked up. And I have seen more than one FX850 break the #2 rod just below the piston, wedge the piston sideways in the bore and lock up the crankshaft