hmm, if u manage to get it started, while car is running, try popping off the oil cap for a bit and see if that causes any reaction.
most notible is the ccvv, they tend to go.
items replace
1, 2, 3, 4, 7.
not being a mech myself, but have worked in parts and service at bmw, its something to look into.
also look at the basic maintenance items, oil change w/ correct weighted oil, fluids topped up or flushed, air filters, spark plugs, ignition coils.
notice any oil consumption issues, check engine lights?