My friends convinced me to buy a flat iron to give myself a new look once in a while. So, I did. I used it a couple of time in one week. Now, after washing my hair and leaving conditioner on for several hours... my curls wont come back!!! HELP!!! What do I do?

My curls exist from root to about four inches then the end inches, about three, are straight. My hair is mad at me.

How do I get my curls back??????