Gordon Snell, Tom's Amazing Machine Zaps Back. London: Red Fox, 1989.
This is actually rather a fun book, it just isn't science fiction. In the first book (which I don't own) Tom's computer becomes infected with Zenda, a personality, and he has adventures. it seems to be aimed at around the eleven year old, which makes it worth noting because that's unusual. This isnt a YA book, its definitely a children's book.
In this one Zenda turns up in a lap top ('only the size of a typewriter'). He and his cousin Emma proceed, with the help of Zenda, to trap a drug dealer and work out why Emma's mother is on the run, and to secure Emma a place in the school football team (desegregating it in the process).
The problem is that through all of this Zenda acts not as a computer, but as a fairy godmother:
she processes sister Marion's drawings to turn them into fashion plates
she does Tom's homework
she tells Emma how to campaign
she eventually takes a part in the school show.
There is nothing Zenda can't do.
I've got some of the others in the series but I won't bother blogging them.