Jelly Bean :: Android Tablet Doesn't Switch Off

I have a problem with my Android Tablet (not sure if Android 4.1/4.2/4.3 but well, possibly). I wanted to use it for a bit, but it froze right when I opened the browser. I pressed the switch button, it went black and then it didn't switch on or did anything at all. After a while, it worked again, not really, but well, it showed the last thing I was doing while using it, but it was still frozen and I couldn't do anything. Now it stays like that and nothing happens. I tried pressing the switch button (together with the up/down volume), but nothing happens. It stays like that, turned on and frozen. My friend suggested me to leave it like that until the battery dies (when I was last using it, it had 40-30% battery left).

My tablet is from a network brand (or whatever it is called), Cosmote (Cosmote MyTab) and it worked perfectly so far ): I'll take it to a service if it still stays like that, but I would avoid that, since my parents will think I did something wrong, even if I didn't!