BMW Repair: car wont start?, vacuum hoses, crank sensor

Question
I have a 2001 BMW 325i.  I recently moved into a hilly area and my driveway is an uphill parking area.  I parked the car uphill with the nose end at the top. ( Im not sure this was the problem) at 4:30 am I was leaving for work and it did not start.  It turned over, battery was fully charged, no weird noises, just acted as if it was out of gas.  I have 1/2 tank of gas, so i moved the car to bottom of hill in neutral to a flat surface.  At 9 am I tried starting it again.. turned over, same thing... would not start.. no weird noises at all still..
At  1pm i got in it and it started right up, no problems at all.  Im clueless to what it was or if it could even happen again?
I was told it could be a crank sensor by the guy at a european motorsports repair shop and he said that he wouldn't be able to tell because there is no service engine light on.  Earlier when I had tried starting it and it wouldnt start, the service engine light was on.  After it started right up at 1 today there was NO service engine light on at all.  HELP!

Answer
Chris, It is possible for the crank sensor to be intermittenly faulty causing you issue, but in my opinion it is not very likely based on the fact that I never see them go bad on your E46 model and engine. The service engine soon light is always on with the key on and goes out once the engine is running and the 'bulb check' is finished unless there is an emmissions related fault. You must figure out what component of combustion is missing when your car doesn't start (spark,fuel,compression). Compression is out of the question because we know your car runs and the motor is mechanically sound. So either spark or fuel is missing from you equation. Let's check for fuel because it is the easiest to check. Get a can of starting fluid at the auto parts store or gas station. When your car doesn't start remove one of the vacuum hoses on the intake manifold or intake boot and give it a quick squirt of the fluid and crank the motor. Don't crank for longer than 15sec. at a time. The vacuum hose on the brake booster is easy to get to. If the engine starts to sputter then you know you aren't getting fuel. You can check spark by removing the plastic cover on the valve cover (two 10mm nuts). Remove an ignition coil and spark plug. Leave the plug connected to the coil. Ground the plug on a good engine ground (piece of metal). Have someone crank the motor over and look for a good spark. Also make sure you have gas in the tank reguardless of what the fuel gauge indicates (we have problems with the fuel sender units).
Let me know what you find.
-Evan