Check your Fuel Filter and Injectors. If that is good check your air intake
Sounds like you might have a bad starter relay.
Turning on the headlights with the engine turned of.
small journal cranks can be ground to a minimum of 1.9585 (rod journals) big journal cranks 2.0685 ( rod journals)
I had a simalar problem on my 99 e320. It turned out to be a crankshaft position sensor. by the way, the engine cranks automatically until it starts (or doesn't) even if you let go of the key and let it return to the run position. other possibilitys include the ignition key
A very basic understanding of how a car starts is. When the ignition key is turned power from the battery flows to the starter motor which turns the flywheel and cranks over the engine whilst this is happening the distributor is turning allowing electricity to each of the spark plugs and igniting the compressed air/fuel mixture. thus starting the engine
It is not supposed to be on when engine is running unless there is a problem.
could be a bad crank sensor, it wont always set a code, ive had a few that dont. if you have a scope or scan tool, manually check that the sensor is good.
There are things called arm cycles, which basically are wheel chairs with a bicycle drivetrain added to them, with the cranks being turned by the arms.
On one had you say it cranks and then you say it won't turn over. Which is it? If it cranks, then that means it IS turning over but just won't start. If it won't crank then it is NOT turning over. We need to know which it is to determine what may be causing this. Repost this with a better description of your situation
Fuel may be draining back into the tank. So the engine will turn over but not start until the fuel reachs the engine. If it is damp out, the wires may be bad. The spark will arc before it gets to the plugs, preventing combustion. It takes fuel, spark and combustion to make an engine run.
It is probably your cooling fans. These are electric and may run with the engine turned off. It is probably your cooling fans. These are electric and may run with the engine turned off.
When a check engine light comes on, it means that there are issues with the engine. It gets turned off when the person resolves the problem that caused it to turn on.