Tractor will not start (does not turn over), Help?

Have a UTG2060H Snapper tractor, Kohler Pro/hydrostatic auto.
It was running fine - cutting the lawn with the 60" belly mower deck. I smelled somthing like rubber burning briefly & thought it was a belt. I sut off te engine to check & it would not start again - just a loud click. As always - the engine was running fine before. I checked to see if it was in gear (it has a hydrostatic auto) by moving the pedal - same result. I removed the body to look at the linkage & found a bolt missing on the linkage for the transmission. I just tried to rig something up to try & start it - but still could not - and the safety switch below seems seems to be functioning (no sound if the linkage is moved above the top of the switch), i removed the mower deck from the middle pto - still nothing. The shaft from the motor to the transmission moves slightly when the key is turned & the clicking noise happens.
Any help would be fantastic.
Could there be something wrong with the pto clutch or could the pto be engaged (even though the electric switch is off)? I do not believe it will start with the pto engaged...
Help...
Thank you,
Bill