I have a Samsung Galaxy Tab S4 purchased recently on a contract with Optus. It has been working fine until this morning when I went to enter the PIN. It accepts the PIN but then keeps returning to the home screen. I can't open anything - apps, email, browser etc. I have tried re-starting and powering off but nothing works.
It sounds like it has developed a software fault.
Have you tried hard resetting it? This sadly will wipe it back to factory default, but if that doesn't fix it. Then it's faulty and will need to go back via an Optus store for repair/replacement.
Thank you, this info is useful. Unfortunately the first step requires turning the device off. I can't turn it off. When I select Power Off or Restart it asks for my PIN. When I enter the PIN it goes straight back to the home screen/desktop.