Hi Orejita de Burro,

You might have removed the user from "Administration / Access Rights" group.

Solution 1: If you have another admin user.
Login with another admin -> Goto settings -> Users & Companies -> users -> select user(who you want to give admin right) -> 'Administration' field -> select settings

Solution 2: Raise a support ticket, Ask to odoo team for the same.
Click on your profile -> support

I hope this will help you.

Thanks & Regards,
Email: odoo@aktivsoftware.com
Skype: kalpeshmaheshwari