car won't crank up on 1995 BMW 525i

My car cranks up when it wants to, could this be related to the oxygen sensor or three way catalytic converter because my battery good

Asked by for the 1995 BMW 525i
The first thing you need to do is find out if there are any codes in the computer that are related to the problem you are having. Unfortunately this year BMW was right before OBD2 was required. You would need a BMW specific scan tool that will hook up to the big round connector under the hood. Some simple things you can check are, if there is a EWS lights on with the key on engine off. If so this would indicate a problem with the Anti Theft system. Also check all the fuses and make sure you have a good battery.
Let me know what you find.

1 more answer
No. If your car won't crank over it has something to do with the starting system. The starting system includes the battery and starter motor. It also includes the control components and circuits of the system. They are the ignition switch when in the crank position , the park-neutral safety switch on an automatic, a clutch pedal switch on a stick shift, the starter relay, fuse, and all the wiring and connectors between the parts.