Not sure if this will help as mine is the V6, but had a very similar issue on mine a while ago...
I found a 7.5 amp fuse (brown) blown in the fuse panel near the drivers right knee.
Now, I'm not sure if the fuse panel in your car is similar to mine, but the fuse was quite hard to see, had to get my head right down in the foot well to see the half a dozen or so fuses at the very top of the panel.
To cut a long story, it turned out to be the immobiliser / key code module that was faulty!
It's a matchbox sized black box with a green sticker that lives behind the dash, kind of between the fuse panel and the steering column.
My local garage had to admit defeat (although they did suspect the module) and tow it to the local Fiat garage.
Another fuse was found to be blown (apparently somewhere behind the glove box) a new module was ordered from Italy, installed, programmed (this has to be done using the appropriate equipment) and I was on my way a little under 300 quid lighter!
Hope this helps!
"Looking through the knothole in Granny's wooden leg"