Lowe's MTD 1997 lawn tractor -sat about 3 years,

Does the engine spin by hand freely? you need to see if you can put a pipe wrench or channel lock pliers on the shaft of the motor and see if it will spin over freely.

Sounds like it is locked up. Could be rust in cyl. or liquid lock from gas, remove the spark pulg and see if it will turn. Try to turn by hand or use a wrinch on the main nut on top. If you suspect rust, remove the spark plug and spray wd 40 in there for a day, try to turn with wrinch back and forth. till you free it up. it may burn a little oil but she should still run. You will need to clean the carb it will be gummed up, no doubt with rust or old gas (old gas turns to varnish in about 3-4 months). if it has sat outside it will rust the cylinder thru the muffler thru the exhaust valve if open,  moisture finds away.