[Dancake]

Details of the car. Year, transmission, engine etc. If it's a D5, the crankshaft position sensor is located at the top of the transmission in a bracket that's bolted to the engine. It's pretty much top dead centre and can be a little tricky to access. The electrical plug faces the front of the car. Because the fault started after you replaced the starter, I would inspect the wiring going to the crankshaft sensor to make sure you haven't damaged anything in the process.

The starter motor earths through the brushes and into the engine block/transmission housing. When changing the starter you should have noticed the little locator stud on the replacement starter. Was it clean and free from dirt and corrosion before you fitted it? The same goes for the hole that the stud goes into. Also were the mating surfaces between the starter and transmission clean? A bad earth can give crankshaft position sensor fault codes because of the electrical interference, and will stop the car from starting. It's worth checking all of your earth connections to make sure they're good.