If the logic board on your MacBook or MacBook Pro is blown up, and you are out of warranty, and don't have a backup, you are not completely screwed. At least you can get your data back.
In principle, it works like this: Take out the hard drive and put it in a 19 Dollar USB enclosure. This way, the hard drive from your MacBook instantly becomes an external USB drive. Now you can connect this drive to your new Mac and access all your files.
If you don't know how to take a hard drive out of the MacBook: there is a cheap and cheerful way Take it to the nearest bookstore at your local university campus. They usually have a technology and repair department. For a few dollars, the friendly technician will take care of this for you.
If your hard drive is blown up: I can feel your pain.