Replying to Laptop +K

I was recently having a conversation with my dad and found out that he hadn't gotten rid of his old work laptops...
He gets a new computer every few years and until recently i thought that he had sold the old ones to help pay for the cost of the new ones.
I'm trying to get him to give me one of these old computer, and he agreed to this, but my mom wont let me have it.  I have a computer for myself in my basement, but the convenience/ ability to transport a laptop would be great.  Also, i would be able to get on NS more easily.
I have already tried explaining these things to my mom but for some reason she wont give in.
To make a medium length story short, I need ideas to help me convince my mom to let me have the laptop, and not just have it gathering dust in the cabinet.
+K for help
Ill keep you guys posted