I'd imagine one of your kitchen lights failed, tripping the breaker and destroying your dimmer in the process. Replacing the switch would be the first thing to try.
If the neon is lit on the fused connection unit then the fuse is good and power is getting to the outgoing terminals. This means that the failing lamp has probably damaged something internal to the cooker hood.
They don't get hot as such but they do get warm, and if this warmth is not allowed to escape it will very quickly destroy the fitting.
Why do you think your installation requires fire hoods? Have a read of our wiki about them.
Do you have a dimmer switch? As you've connected both reds and both blacks together you've created a perfect short circuit which 1000's of amps will have flowed through destroying any dimmers sand possibly even a normal light switch.
It looks like that socket is part of an old conduit system.
You should be able to unscrew the lock ring from the conduit with a pair of grips but you must replace the back box with a new metal box with the conduit securely screwed back in place. The point fed by the conduit relies on the...
Which ever method you find easier is fine. It can be quite tricky to get all the wires into one central jb so a small joint at each light may be easier.
Remember that all joints must remain accessible for future maintenance and testing.