external usb hard rive will not show up

[pspmixer]

i recently done a full system restore on my desktop computer and now my external hard drive wont show up in my computer , it says format hard drive to view but dont want to format as it has things on there which i need
i have tryed on a xp laptop and the same problem comes up.
i also tryed assigning a drive letter but that just kept on coming up with format drive, so i remove the assigned drive letter
any help will be greatful for thanks