2010 Impala wont start after never having any mechanical issues.I replaced the battery-no luck.Checked all the fuses.Then replaced the starter.It now makes a clacking sound when trying to start.But never starts.

I had it towed to a mechanic who said it looks like the motor is locked and needs to be replaced because the flywheel isn't turning.However the car is full of oil.
Any suggestions on what this could be.BTW I damaged the oil sensor while replacing the starter.Don't know if this will cause it not to start.

 

When you say not starting is it turning over and not firing or just not turning over?

I ran across a 2002 Impala that didn't turn over, no solenoid click. It had a bad crank relay on the right-front fuse center attached to the strut. Replacing the relay fixed it right up.

Of course, your motor could be locked up as well. If your anti-freeze at the proper level? Could be hydro-locked if you have a cylinder full of liquid.