Engine's in and plugged up but isn't starting

It's getting a spark, fuel and air but just not taking. Flames came out the back of the manifold so something's happening but just not starting???
There is one plug I can't find where it goes - didn't have time to have a proper look (I've attached a photo) it's the NS behind the battery? But doubt that would stop it from starting though. Would there be something from the ECU stopping it from properly starting but still allowing it to turn over?
I'm away for a couple of weeks so its going to have to wait until I'm back though.