Help please!!

[Hayes2014]

Earlier on I was out putting exhaust assembly paste to try stop a blow on my shitty Toyo manifold for the NCT,

All was going well put the manifold and turbo back on started car up to warm up the engine to dry the paste,

Then I jacked up the car at the rear to check for any more little blows or anything, turned off the car after about 5 minutes anyways left it off for another 20 minutes or so an went to turn it back on an it wouldn't start, thought it was just out of juice because there was very little in it as it's just been parked up for the last 6 months or so,

Went an got fresh petrol put it in still no good,

Now there is black smoke coming out of the exhaust when it's turning over,

It's getting petrol and spark

Would there be any chance some of that exhaust paste could have went hard and got in and bent a valve or something ??? Because as it's turning over it will turn over fine then stop and then start to turn over again ?

Any help at all apreciated

Thanks:)