I can't replace my damaged my I3 disk drive with PC's HD disk drive ...why? and also the backlight of LCD was light off I think it must be changed.. how to slove this problem.
... Did anyone knows how to add harddisk drive into my i3...

From what I've read (sorry, I don't remember where) and from studying my X3's disk drive, you could replace it with a low cost PC disk drive... But a special connector should be built for it: My X3 drive has one flat cable for both signals and power feeding.

LCD backlight is limited to some thousand hours, and it could well be that its lifetime has passed. If you are not afraid of opening your i3 , unscrewing and unplugging, you could change it yourself (I speak again from my experience with the X3, but I don't think it should differ very much from your i3).
I hope it helped...

Do yo know which connector to change the cable. When I try to change my Disk drive with PC disk drive the LCD is off I think its because of connector. but.. how to matching the connector