Last night I struggled to get my 86' 325i started... turning over but not firing into action straight away...after 3 or 4 tries it fired up but there was a "pop" sound from under the bonnet...drove fine...
Today nothing...turning over but no matter how many times I tried during the course of the day it did not fire into action...
You'll have to narrow it down a bit further than that!
Sparks at plugs?
Fuel pressure in rail?
Fuel pump running when cranking?
Plug tips wet after cranking?