truck will not start

my '94 blazer tahoe will not start. we had noticed gas in the oil. we changed the oil, it has a new battery and starter. it will spin, but not run for more that 5-10 seconds, it smells like gas when we try to start it. any ideas? I have had some suggestions, but the mechanics I have talked to said some of things will not affect it starting. (i have another post on here, but cant figure out how to change the subject...