Mower was running shut off now does nothing when i turn key

You'll need to check all the safety switches. Probably one in the seat, one for the mower engaged, one for clutch/parking brake engaged, possibly one for reverse gear selected, and possibly for position of the steering arms.

Check that the interlock on the seat is connected. Mine failed in the same way a while back and all that was wrong was a broken wire to the interlock switch on the seat. This is designed to stop the engine if you get off the mower.

most likely yes but what brand/model do you have ???

Is the small wire, coming from the Ignition Key, Getting 12V to the Relay when you turn the Key? Were Mice chewing on your wires?

The ignition switch takes the coil grounding wire to earth to cut the motor, so there is either a problem with the ignition switch or a break in the earth wire ( check the conections down by the engine ) to check the system run the machine with the deck engaged lift yourself out of the seat, if the engine stops it will be more than likly the ignition switch playing up, if it does not shut down there is a wiring issue.

if you need to jump the solenoid to start it and it shuts down sounds to me that you have a bad safety switch start with the one on the pedal

sounds like your battery went bad...try a battery charger and see if it works that way ..if so then bad battery or not charging the bat. when running

Rally tractor mower won`t start. Battery fully charged but nothing when turn key

ran into this problem twice this season, about drove me crazy - finally traced the problem to the anti-backfire solenoid [the little cylinder at the bottom of the carburetor that holds the float bowl on] - after running fine for 20 minutes or so [it varied], the coil would release the plunger and shut off the gas flow. as soon as you turned off the key and turned it back on, it would start back up - replace the solenoid and problem vanished

The problem requires a service tech. There are many reasons for the problem They can range from a battery that has gone bad to a relay or safety switch under the seat etc. Again the lever issue can be many things.