how to backup harddisk ?

You can do several things. You can buy a pile of CD's. You can buy a slightly smaller pile of DVD's. Or you can buy a large USB external hard drive if you have USB capabilities on your computer. Some of them are quite big, get a 300 minimum. * This is an example of such a hard drive. * http://www.amazon.com/Western-Digital-Firewire-External-Option/dp/B00092CKA2 * Or you can do a combo variety back up, if your computer is backed full of media, pack your media into DVD's or CD's and pack your data into an external hard drive. * Please remember, I am making a number of assumptions about your computer. I'm assuming you have USB 1.0 or 2.0 and a CD-DVD burner. If I am incorrect, I apologize.