Background lighting gone crazy

I just bought the phone 3 days ago. Everything was fine until I decided to download some games from the internet directly from my phone, into my phone. Everything was OK. After that too, but when I started Super Mario, I simply couldn't exit the game. So I turned my phone off. After that I wanted to start PhotoQuestPhishing which was on the phone when I bought it, it simply displays a white screen and the entire display closes. After 2 seconds the display comes back, but no backlight, no matter what buttons I press. The interesting part is, that if I go to Settings->Display->Brightness and I move the bar to the left or right, the backlight simply turns back on. I also noticed that if the keys lock, the display starts to dim, and after a while it turns off the backlight. This is normal. But when I press unlock it should return to full strength, instead, it comes back only to dim mode. After a few seconds, if the keys don't lock, the dim dissapears automatically and the display comes back to full lumionosity. And I don't do anything to it. Another thing is when it's under charge mode, the display doesn't light up, only if I go and move the bar in the brightness section under settings->display. I went accessed the service menu via ->