My son likes playing game on his computer all day and I can't make him stop playing without getting angry. He's 9 y.o. What should I do to make him quit playing without screaming?

Here what i do with my son,9 y/o too: 1)set limit - he can use comp 30min per session, only 2 session per day. 2) he musy do house chores to earn his computer sessions, eg clean up the dishes after meal. 3)make sure he has other things to play with, ie wooden blocks/ craft set/building set etc. 4) during his computer session, i'll remind him 5 min ahead that the session will finish and he will be doing ... (fill in the next activity you plan for him). Therefore he knows what he will do next This takes practise to get him familiar with your rules.

Getting angry is normal but you need to apologize to him quickly

Don't worry, he will get bored soon