Ken's right, read the codes first and see if the car will tell you what's wrong. The crank position sensor is one of those that's hard for the normal backyard mechanic to check. You have to check the waveform with a scanner or oscilloscope and make sure amplitude and frequency remain consistent during crank, and you can check the resistance against specs with an ohm meter. Most guys I know try to eliminate other possibilities, then invest in a CPS and see if that fixes it.