Impala,When I go to crank my car the key stays in the start position and the car is constantly trying to crank itself.

When I place the key in the ignition and proceed to crank the car the key stays in the start position and the car is constantly trying to start itself up but never actually turns over. I then have to manually turn the key back so the car can stop trying to start up. I have had the fuel pump replaced and the crank position sensor. The car worked like normal for one entire day and then the same problem reoccurred. Though I don't think this is the problem but each time the car wouldn't start it was parked on a semi incline in our driveway. But we have parked it her numerous of times befor