Re: starter won't disingage
disconnect the big wires on the solenoid. (once again, write down/mark the wires or take a pic so you can put it back together). The one side will go directly to the battery (or alternator). The other side to the starter. See if there is continuity between the (now empty) posts of the solenoid.
If yes (without power) >> it's stuck and needs replacing
if no >> turn the ignition on and (little wires connected here) see if it "clicks".
MAKE SURE YOU DO NOT PUT THE HOT (12V) WIRE (NOW EXPOSED AND NOT HOOKED UP) ON / NEAR ANY MEATAL. YOU CAN ARC WELD WITH A BATTERY (ask me how I know

) AND/OR BLOW IT UP