English Trainer Chronicles: Guessing nothing

Learner: It's good to all time change of computers.
Me: You have to fix your sentence. It's good to ...?
Learner: It's good to change of computers ...
Me: No "of."
Learner: It's good to change about computers.
Me: Not "about." Change what? What do you change?
Learner: It's good to change on? To? For?
Me: Just say what you will change.
Learner: It's good to change ... computers?
Me: Exactly! Good!
Learner: No of? To? About?
Me: None.
Learner: Bah. It's hard to guess if there is nothing, no?