For Testing Power Button, there is option in our Samsung Members App to know whether its software or hardware issue.
1. Click Plus button in Circle, botton right of Samsung Members App. 2. Click "Phone Care". then Click "Interactive Checks" (Give all permissions). And then click "Hardkeys". Then test whether your Power button is working in that test or not. If its working in that test then its software issue otherwise hardware.
So whatever the result is try this step mentioned below.
Do this Thing. (Data will be safe)
1. First Switch off the Phone, then Press and hold Power Button + Volume Up (Simultaneously), as Samsung Logo appears release the Power button but keep holding Volume Up.
2. "Android System Recovery" will appear, you have to control the functions with Physical buttons. Select, "Wipe Cache Partition" with Power Button. Select "Yes".
Wait for the system cache partition to clear.
Select the Reboot option to return to normal device usage.
Hope it helps.
If this Doesn't work, Try with Factory Reset. (Data will be erase)
