Help with behavioral questions

So my Superday to SA offer rate is about 50%. I noticed that the "Tell me a time when..." interviews are the ones that I don't receive offers. I stress working on team projects and with others but sometimes I feel like I may have said something that got me dinged.

"Tell me a time when you had a disagreement with a coworker?" I tried different variants of answering this question and I guess they are all wrong? Do I approach them politely and try to work it out? Tell them manager? I don't know.

And the ones I hate the most are...

"Why should we hire you?", "Why do you want to work here?", and "What makes you different from the other candidates?"

Most of my interviews have those 3 questions and it's a 50/50 chances they'll like my answer. In a room surrounded by highly intelligent and capable Ivy league candidates, I, a guy from a non target school state school cannot really answer that question beyond saying just that... and I speak Russian so there's that.

I'm just not sure what they want to hear from me. Most of us haven't done anything substantial yet, I haven't done anything substantial yet. I just want the opportunity to do something meaningful and to start my career.

All tips and tricks are helpful (I bookmarked some of the other threads already).