Ok - renewed effort to get it back alive and running.
Having had it sat for too long, but with a charge + jump pack being able to get it running again - i thought, optimistically, i'd swap for a fresh battery, get it MOT'd/taxed and service it before snetterton on 13th (where it previously lunched an engine... confront it's demons head on and all that), and give a friend an opportunity to try it out for track use.
I swapped the battery, and despite what i think is a threaded battery hold-down clamp bolt (how the fuck you are meant to access/fit these anyway, nevermind fix it if it is threaded..?!?!), and despite the battery box being a fucking nightmare to work around, i've flipped the battery in and hooked her up.
hit ignition, turns over once, fails. now wont turn over at all (it's not even trying). ignition on just results in an electrical whining noise behind battery/engine (firewall area?), but no radio or dash lights anymore, despite the battery having a charge. jump pack made no difference, somewhat obviously as it's not a dead battery issue. ive had it on trickle charge to ensure it's fully charged but again not sure this is really the issue. seems like ecu/electrical/something.
my local car shop/mot place is going to have a look, but they're not renault guys and i don't hold out much faith. i think they'll just tow it back to theirs, get stuck and waste 3-4 days whilst i could probably solve it with some useful insight.
any ideas what it could be?
obviously rejigging the battery box to get a battery in means i could have knocked something in the various battery-box-attached-ecu-etc-connectors, or the immobiliser is dead, or something?
i noted i can turn hazards on, but not headlights, and nothing i do brings up dash/radio/etc lights/instrumentation.
it will lock/unlock on the remote.