It sounds like the new head gasket isn’t working properly and the car is still overheating. Or, the root problem wasn’t the head gasket in the first place, or that the mechanic missed something crucial that allowed the new head gasket to fail almost straight away.

Was the cylinder head checked for straightness? Was the cylinder block checked for cracks? A warped cylinder head or cracked block or bore can give symptoms just like a failed head gasket, but replacing the gasket won’t fix them. I think you need to have a deep and meaningful conversation with your mechanic and work out a plan to either dig further into the engine or replace it with a second-hand unit that’s been tested. The latter is probably the smarter, cheaper way to go. Either way, though, you risk spending more on the car than it’s actually worth. Maybe it’s time for something newer, more efficient and safer, not to mention more reliable.

He shouldn’t have done anything without disconnecting the battery. The computer is the component that senses a crash situation and moving it has caused it to set off the airbags. My view is that it’s the mechanic’s problem.

Tyre fitters will often recommend higher tyre pressures as it can improve the handling, but 36 psi would seem too high, particularly in a little car like the Barina. I would run them at 30-32 psi front and rear.