"You cannot prove anything in science"
You can't?
Does this mean my computer really isn't here? And isn't working?
It means that the scientific principles that led to the development of your computer are merely the current best models to fit the facts, and not indisputably proven facts.
No, you can't. Proof is a mathematical concept. In science, you can state with a high degree of certainty, but you can never prove.
Does this mean my computer really isn't here? And isn't working?"
Why don't you prove to us that it is?