My daughter is 14 and I've just found out she has a boyfriend behind my back, I Signed into her MSN account?

Your daughter is old enough to have a supervised relationship. Selling her laptop and grounding her would be an unreasonable punishment for trying to have a relationship with a boy. You did intrude on her privacy and it is unlikely that grounding her would repair the betrayal she will feel. Try explaining to her why you don't want her in a relationship and then try to teach her how to have a safe one.