Chosen Solution
After successfully replacing an iPad Pro 9.7" screen with no issues there power button/volume buttons do not work. These are different flex cables so this tells me something with the screen is potentially preventing the functions. I have disabled sleep/wake feature but this does not resolve the issue. Also, oddly enough with the accessibility on the on screen power button and volume buttons will not work either. I have reconnected the old screen to see if it was a screen issue but the buttons still do not work. The power button will turn on the iPad initially as well as wake the screen but it will not put the iPad to sleep nor will it prompt a power off if held down. Any help/suggestions? The battery was disconnected prior to any other cables were disconnect and physical everything in the device is clean and connectors inspected.
I wonder if you have found a resolution to this issue. Based on what you say, you have tried the most obvious things. I would try a Hard Reset and if data retention is not an issue, a full restore.
Thank you DC Tech for responding with your solution. I had the same problem with an ipad mini 2 with ios 11. All i had to do was plug the ipad into itunes and as soon as itunes recognized the ipad the problem was fixed.
