be (become) interested in
Dear Li Hua，
How are you? I know that lately, you always play computer games. That’s why you can’t do well in recent exams. As your good friend, I hope I can give you some suggestions.
First of all, I think you should understand what things you need to do. As your age, studying is the most important, you shouldn’t give up your dream because of computer games. Do you think so? If you can concentrate on studying, you must do it well, Also, when you want to play computer games, you can try telling yourself that you shouldn’t do it any more.
And you should find the joy of studying. You had better study in some interesting ways. If you can use the way you like to study, you may become interested in studying. It’s helpful for your study.The most importantly, you will not always think about computer games! Besides, If I were you，I might let my parents supervise me to use computers.
That’s all. In short, computer games are bad for you. You shouldn’t play computer games so much that it causes some bad influence on you. I hope my suggestions can help you. And I hope you can do better in exams.