car blowing white smoke out the intake, and wont start ideas repairs?

my 1996 grand cherokee laredo straight 6 4l was running at one point... my sister borrowed it ran it hot and left it on the side the road for a long while... recently went and got it. when i try to crank it the starter turns but the engine wont catch and start. everyonce in a while the engine will blow a white smoke out the top of the engine. me not being mechanically inclined what would be causing this and what can i do to fix?
around 250000 miles