I have. a 1542g sabre jd lawn mower will start and

Clutch switch is bad.

You probably have a broken linkage that is not allowing it to disengage look around on your full lace on your mower deck you may be able to drop the deck by removing some other clips and pins Jack the front of the tractor up in the air or suspended it from wench

simple things to ck first :
(1) battery - fastest way to test it is to jump start it
(2) safety's - with tractor off , turn key to first click , then try and engage the mower deck , you should hear a click , shift to 1st gear try again you should not hear click ,back to neutral then hold clutch down , try again you should hear click , all of this assumes your sitting in the operator seat when u try it , as the presence sensor only trips on human presence over 60 lbs if any of these tests does not produce the desired effect check that safety sensor , although ive found on JD's the seat switch is found bad allot

Sound like a safety switch has gone bad. Either the clutch or seat switch are bad.

Keep your clutch pedal depressed when you engage blade3 or put in gear.Good Luck!

Almost certainly it is the park break switch,i would start there.

http://www.askmehelpdesk.com/attachments/tools-power-equipment/21055d1245605830-sabre-38-deck-belt-routing-1438gsdeck.jpg

it sounds to me like the valves on the mower need to be set which will probably need to be carried to a repair shop. jd

your lacking power and probably need to clean your carb or adjust the main idle screw..its on the botton of the float bowl...back it out a half turn...start with a quater..well its running

I think that it is not imposible to switch gears it is just very hard. i had that problem once too!