If your stairs are manufactured by Kwikee , there are three fuses in the system in various places, through out your coach , any one being bad will stop operation, then there's the possibility of a bad lock out switch.
If you go under the coach there should be a manufacturers tag near the motor and gear reduction housing.
If you don't have a users manual for the steps, and they're not Kwikee, please confirm the brand and re-post.