Cadillac Repair: trouble shoot starter, crankshaft, cts

Question
cadilac 2005 cts  at turn ignition it clicks i turn/rotate crankshaft than it starts shall i replace starter or continue to truoble shoot

Answer
IS or HAS the CHECK ENGINE light ever illuminated while driving the vehicle and or has any other lights illuminated or any messages from the message display center ?.

What work or diagnostics of ANYKIND WHAT-SO-EVER have been performed on the vehicle trying to fix this problem ?.