if anyone could please help me shine some lite on this,
I've replaced a sensor underneath the alternator assuming that is the crankshaft potion sensor (?!). I've googled images to see the location of that, there was one sensor that is underneath the oil cap, what sensor is that that? and what was the one i replaced ?! im getting CEL p0335.

 

Yes assuming you have a bugeye per your username, the sensor under the alternator is the crankshaft position sensor. The one by the oil cap should be the camshaft position sensor.
Just because you're getting the P0335 doesn't mean the sensor itself is bad. The code is for a circuit problem, so unless the sensor itself is electrically open the actual problem may be with the wiring. Check the connector and harness. If you have access to the service manual there is a troubleshooting procedure to follow for this code.

 

I have replaced that sensor once before, the code pops up from time to time. lately the car will run fine all day and then randomly it won't start?! and i have to keep turning the key and eventually the car will start