Help meee( Leblanc's main :D)

I currently changed my Laptop to Envy HP the latest version, and I don't know while everything seems so good til the log in into the game (after champion select) my screen flashing in and out the client so bad, and after about 5 times like that it automatically restarts my laptop. I was not able to play the game because the restart time was too long, now Im banned for 20 mins into game. Please help me.