Restart/Shutdown problems with my new Toshiba Tablet

Hi all,
Recently I bought a new Toshiba Encore WT8-A32 8-Inch 32 GB Tablet with OS Windows 8.1. This tablet is amazing.
But recently I started getting restart/shutdown problems with it. When I press the Windows button, it is vibrating, but the screen is not at all responding. Even for If I shut down it vibrates, but nothing happens. When I press the power button for a few seconds, then only it will shut down.
Anybody experienced this type problem before? Your input and suggestions are greatly appreciated. Thanks a lot in advance and regards.
