car wont start

so what do I check or do ?

Compression test and/or leakdown test.

I found one like that on a car by pulling the spark plug, making sure the cylinder I wanted to check was on the compression stroke and shoot about 30 lbs of air in the cylinder.
I could hear the air coming up into the intake.

It made the engine turn over a little because of the air, but it was an obvious rush sound in the intake at the same time.
Compression test on that cylinder was low and I wanted to find out why.:D
(burned intake valve and seat not sealing)