Why is my power button not working

@mubeen1488 see if the power button is still working properly on the power button flex. If it does and tries to close the contact but nothing functions, then I suggest you replace the power button flex. The flex is available at plenty of online stores, the only issue is that there are no guides for this for your model.You could try some of those teardown videos like this. If nothing else it will get you into your phone.

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!