Hi while I was doing clutch in fiat I had battery out for a week and now it won't start, any one know how to get past this or bypass imobiliser or disconnect it completely

It's a 53 plate 1.2 active tried both bus keys an doesn't make a difference, even a good battery

Blue keys

Immobiliser's are designed not to be bypassed or disconnected so doubt you will have much luck on that.
Sounds like the car has lost the key transonder details stored with in the car computer system and may just need the transponders being re-learnt although having diagnostic equipment such as registerd version of multiscan software would give further details, there are some details in the link below that also contain other usefull links for emergency start procedure should your car allow that function and you have the 5 digit electronic security code only available over the counter from Fiat.


https://www.fiatforum.com/stilo/354063-immobiliser-replace-ecu.html