valves,Car won’t start after doing valve cover job.

Once the valve cover gaskets were replaced with new ones and the covers put back on, I put the intake back on without using new gaskets and the car wouldn't start but I did get a pop and a backfire and the intake has become quite warm. I have bought new intake gaskets but have not installed them yet. Can u help

My car has 152000 miles.
My car has an automatic transmission.