Craftsman not starting

My apologies if this has already been addressed elsewhere. My son poured gas into the oil tank last fall. Stupidly left it over the winter. Drained the gas and oil last week. New oil, fresh gas. Changed the spark plug too. B&S 110P02-0003. Every full pulls a 'puff' of white smote cough out. When I pull there is a clanging sound. Doesn't start at all. Next step? Thanks.

If it has not been run like that you should not have too many problems.
Remove the spark plug & put some oil in the plug hole.
turn the engine over by hand a few time to get an oil coating on the barrel.
Drain the oil again and replace it and after you get the engine to run you will need to replace it again.
Catch this oil and have a good look in it.
If there is rust then the engine will have to come apart.
Remove the rocker cover and make sure the valves are going in & out , good chance they have gotten stuck.
If one is found to be stuck, remove the rocker and check the pushrod, good chance it will be bent or even missing