System Disk

[brad]

Hello,

Recently the hard drive in my laptop running WinXP Pro
crashed. I have an external USB hard drive that I copy
the entire hard drive over to once a month. When I got my
new hard drive for the laptop, I connected it and the USB
drive to another computer and copied everything from the
USB drive onto the new hard drive. I thought I could then
plug the new hard drive into my laptop and have everything
run just like it did on the last day I ran the backup.
However, when I put the disk back into my laptop, it says
it is a non-system disk and won't boot. Is there any way
to make it a system disk without erasing everything off
the drive? Any suggestions would be appreciated. I
basically just don't want to have to re-install
everything. Thanks.