2012 Fiat 500 pop. Recently had engine replaced by mechanic with a "new" 35,000 mile engine car has 120,000 miles.

Replaced starter but no difference. Car does everything it should everything powers up and on but engine does not even attempt to turn over. At a loss of what it is fuse relay ignition? Fuses don't look bad?

Immobiliser?

What is an immobilizer?

Watched a couple videos. .. thoes cars all still tried to start my car doesn't. No response from engine at all. Drove fine around town made a few stops then nothing.

Body computer, engine ECU not recognising key? How much of the engine was new?

Have just just had the engine replaced and it won't start on have your replaced it a few week ago and run it for a while now it won't start?

It drove fine a few weeks. I'm not sure how much of the engine is new I had a blown head gasket with warped heads. They they rebuilt it had heads re machined new timing belt new battery new radiator new hoses new water pump the car has 120,000 miles the rebuilt head gasket failed after a month or two. Mechanic "replaced the engine" with one that had 35,000miles on it. Car responded to key fob for lock and unlock and electronics turn on no codes are showing up on reader.

KatTastrophe said:

What is an immobilizer?

Click to expand...

Its a electronic device that stops the car being started to stop it being stolen, in the UK they're standard on all cars, if it fails or cannot recognize the key(there's a tiny chip in the key that talks to the car without needing power itself) then there's no chance of starting often just doing what yours is, but don't assume its this, could be many things.
Have a car auto electrician look at it not a mechanic, its probably a simple fault.

If you try to start it is there a "loud" click when you turn the key to crank it over or silence?

Do the dashboard light up
Do you hear the fuel pump prime when you turn the key
Do you get ant sound then you try to start the car e.g starter motor turning