I used my Hitachi XL 2000 with my HP lap top than my HP dead. I got another lap top (asus) and tried to connect it to hard drive. The hard drive asks me to reformat it. I didn't do it since I afraid to loose all my data on it. What should I do?
When Windows says a drive needs formatting when it contains data, it's a bad sign.
Almost always the drive cannot be formatted anyway, even if you wanted to, because it is usually faulty or has failed.
Test the drive to establish it's state of health. You can test it with Hitachi WinDFT if you are not actually running Windows off it whilst testing it: http://www.hgst.com/support/downloads/