Check out this thread if you haven't already. 🙂
I had the same issue, and I tried many things (buying a new computer to try to break that one, calling a repair service anyway, sabotaging, salvaging for parts, moving it into and back out of inventory). Ultimately I was able to complete the task with some magic spells, which of course will only work if you have Realm of Magic and have these spells unlocked. I selected "magic" then "spells" then "zipzap" to break the computer. I then tried having my character fix the computer, but the repair task wouldn't end. I tried calling the repairman, but they were also endlessly fixing. When I dismissed the repairman it marked the task "repair or replace computer" complete. The computer still looked broken so I selected "magic" then "spells" then "repairio" and now it's functional again. I was able to complete the quest after doing these steps.
