wow... this post is all over.
1, do you have a non oem key-turn to start igntion?
is so.. the oem solenoid will NOT work for you.
also.. if you have a 'car' type solenoid.. the oem thumb button starter will not work for you.
voltage regulator has nothing to do with starting.. not sure why people investigate rreplacing it when their tractor won't start. might as well check tires too?
pull plugs.. add a lil oil down them..
now.. put in neutral. block clutch.. not jumper around solenoid with a big pair of pliers.
does she spin over freely?
if so.. good.
plugs were out to check hydro lock.
oil was for a lil lube.
now.. if she spun.. put plugs in.
depending on what type of solenoid you have.. you will either have to ground a 3rd terminal, power a 3rd terminal, or add power and ground to a 3rd and 4th terminal.
units needing power to a 3rd and a 3/4 'bypass' style solenoid, you cannot use the thumb button ( ditch the solenoid )... these typically use a key to start setup.
post back some details