E39 refusing to fire

Wife driving, noticed very strong smell about 1/2 mile before engine died. No warning lights or error codes, all electrics working ok. Tried to start but engine just keeps turning over without firing.

Is it immobilizer problem ( I have reinitialised keys )
Is it fuel line problem- how do i check.
Are the spark plugs firing, how can i check without dismantling lots of stuff,
Was the smell a burnt electrical item eg relay ( also where are most of the relays, are some inside?)

Checked fuses, all ok.

oil, water, fuel (3/4 tank) all ok.

Any ideas ??

Coming up to xmas and most places closing for holiday period. Would appreciate assistance.

Thanks

Saleem