What motivates you to put forth your greatest effort? Describe a situation
In which you did so.

I know what motivates me and how I would answer it, but I'm not interviewing at the moment. ;)

I'm assuming you're not sure how to answer this yourself? Think about what motivates you to do a good job. Then, try and think of a time at your previous job when you needed to pull from that internal motivation in order to complete a less desirable task.

I hope that helps... I may not be understanding you correctly, but it's a personal question that only you can answer for yourself, I can't really put the right words in your mouth.

How to introduce myself?

Well I guess it would depend on your personality. I am and obsessive compulsive person and a challenge really motivate me. Something difficult to task that others would be leery of trying. I will work obsessively solving problems and creating solutions. I get such a rush after accomplishing something like that.

Not sure if this is a good answer but whatever your personality I think you want to present yourself as a go getter.

What motivates you to put forth your greatest effort? Describe a situation
in which you did so.
I object to these kinds of questions - depending on the mood I was in, I may very well say that my greatest motivation was having nothing better to do than attending an interview where stupid questions were asked!