They're an expensive piece of technology - someone's bound to have left one unattended.
Northforest is clearly the wealthy part of town, so the citizens' homes may prove useful again.
Try checking streets that characters live on.
The principal's house being locked earlier still strikes me as suspicious - he's probably got more stuff we can steal.
Follow these hints if his house is locked.
Its monitor has seen better days, but the principal's setup includes a brand new Commodore 64!
Unlike his fish, this is easy to grab - it's basically just a keyboard, after all.
We have a computer! Take it to Ralf and use it on him to hook it up.
Oh, right, electricity.
To switch the computer on, we need to fill up the generator.