If I understand your post correctly, you could not start the saw but you were able to pull the cord and turn the engine over. Since it would not start, you took it to a shop/guy who fixes small engines, and when you retrieved the saw, it was locked up.
Are you sure the brake is not engaged? Pull it (that black thing in front of the top handle) back, toward the motor. If clicking the brake on and off does not free up the saw, then you need to start taking it apart.
Throwing parts at a machine without knowing what is causing the problem is not a cost effective way of fixing what is wrong. You might accidentally get it working when a simple adjustment was all that was needed.