Use his obsessions as rewards to get him to do other things. My son is obsessed with some U tube video's also (he is seven), can load them up and everything. At school he has a written visual schedule on a white board (he can read but you could use pictures if this boy doesn't) with all the activities he has to do that morning (journal, math. gym etc.) the last thing on his schedule is his computer time. As he does each activity he wipes it away when everything is done he gets 10 minutes on the computer. This 10 min computer time starts his next schedule eg; 10 minutes computer time, lunch, recess etc. His most favorite and often obsessive things start and end each mini schedule as the day goes on to motivate him. At home I don't use a written schedule but I almost always use the "you do this, then this happens" kind of language to make sure he is always prepared and knows what is coming next. It can be hard to get him to do new things, but often once he tries something he loves it....they can even turn into the next obsession sometimes!
My son always has something he is obsessed with, sometimes it is just a fleeting obsession other times they stick around for months, we accept that is part of who he is and use them as rewards to get him to co operate with trying new activities. Often 5 minutes is all the boy will tolerate with something new, keep persevering, 5 minutes of something new then 5 minutes computer, be firm he will not want to stop the computer after 5 minutes but stand your ground, break his schedule up into new activities with the "reward" activities, refer back to the schedule if he gets upset, remind him when this task is done he gets to do his favorite thing again for a while again. Best of luck.
I'm not sure how to lock certain things. I tried it and it didn't work for me...the thing is it's not my computer to really do too much on. I only work with him so it's his parent's computer. I teach him and I find the computer would be an amazing tool that he could excel in if we could just get past the obsessive part. He doesn't want to do anything else but what he wants to do. He will let me get to a website with a program and do it for like 5 mins until he just gets mad.
hello...cant you lock certain things out in the computer? or pretend that the computer is not working...or you forgot to pay the bill..try to put him in a class for something else.like swimming get to get his mind preoccupied with something else..try to see what kind of things they have to do for artistic kids his age..maybe you will get lucky and find something..