The power off/on is not working

@jeananchita most common issue is a broken flex cable. Replace the power button flex cable and re-evaluate. Since iFixit does not have a specific guide for that, use something like this video to work on it. Replacement flex cables are readily available at many online stores.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!