Computers are a specifically engineered thing, they are not the sort of object that evolves naturally, at least not as an initial step (the first step is autonomous nourishment and, you know, motion). Silicon-based life forms would likely not be computer-like at all. They would probably still extract energy from oxygen and various other chemicals, they would have their own bacteria and fungi that eat and decompose silicon compounds, and they would probably still not survive in space.

Also, even though silicon has interesting properties on its own, carbon is kind of just better at everything else. It can make bigger and more stable structures, for example. Its oxide is also not, you know, a stable and unreactive solid. So it would be surprising for life forms not to use carbon extensively, unless it was much too rare, and in that case I honestly doubt it would get very far. As a building block, carbon is just outstanding, there is a reason life on Earth is based on it even though there is a thousand times more silicon than carbon on the planet.