I cannot turn on the screen again

I purchased that tablet: Tablet Motion Hold TR72

The Android is 4.2.

In my smartphone, I'm used to click the Power button in order to lock the screen before put in the pocket. When I do it in that Tablet, the screen locks, and when I click again the Power button the screens doesn't tuns on again... I try click the "Home" buttom too, but it doesn't works.

When the system is unlocked, I click the Home button and it successfuly goes to home screen. And the power button obviously works because I can turn on and off the tablet.

I suspected that I turned off instead of lock, but after some seconds holding the power button, I can listen the sound of the tablet turning off. So, I hold the power button again and the tablet fires again.

So, I wonder that can I'm missing some really basic step or configuration or command in order to see the unlock screen again...