Samsung Tab 3 10.1 P5210 (screen goes off than return back on a second)

Hi guys,

my English is not perfect so I apologize for my mistakes.
I bought few days ago Samsung Tab 3 10.1 P5210. I can´t reutrn it from many private reasons.
The problem withy my Tab 3 makes me so nervous. When I use it for a while (display on), very often my screen goes off on a second and then return back. Practicaly Tab 3 is uselles when that happening. I have notices that when I watching a movie on it, Tab works perfect. When I checking my e-mail of fb or instagram, or even surfing sreen goes off and than back on.
I have done factory reset and hard reset too but the problem is still active.

I hope someone can help me and give me some advice. Thank you so much guys. :D

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