Urgent help! 2002 Vectra with padlock/immob light on.

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Desperately trying to help a friend who can't really deal with the £600 being quoted by the main dealer to fix his car.

2002/52 Vectra (C I believe?) that won't start, shows padlock icon on the dash.

I've had a read up and it seems that the chips in the keys can fail and or the CIM (?) unit in the steering column. I'm waiting to speak to my friend to understand fully how it's behaving.

Has anyone any advice on how to try and diagnose this? I've found tales of everything from fuses to flat batteries causing this behaviour!

Thanks