There are two major occasions in which you can decide to destroy Stefan's computer (and his dreams). The first is mentioned above, when his father is trying to coax him out for lunch. If you decide to pour tea over the computer instead of yelling at his father, that's it, game over.
The second is a bit later; Stefan has one last weekend to make the game perfect, and his computer crashes. You can either smack the desk or smash his computer. If he smashes his computer, though, the jig is up.
This ending is only slightly better than zombie medicated Stefan, just because there's a tinge of crazy there. At least there's a bit of passion in his motives! And hey, maybe he could buy a computer and start over. Or something.