|You may need to change settings in the bios Setup in order to boot from the correct hard drive if you have more than one hard drive connected.|
- there is a list of hard drives, often near the Boot Order or similar settings - the hard drive model you want to boot from must be listed first
- or - less likely - there is no list of hard drives but there is more than one hard drive listed in the Boot Order or similar settings - the hard drive you want to boot from must be listed first. If the hard drives are not listed by their model numbers they're listed generically - e.g. HDD0, HDD1- according to the order in which the bios detects them and according to which headers they are connected to and/or how they are jumpered
"@Jefro, I m not sure why you think "You can't boot xp to a usb."
I booted mini windows xp (Pe) many times from my USB stick (Transcend 8 Gig)."
You may be able to boot that from a USB flash drive, but I know for sure you can't boot an installation of regular 2000 or XP from an external hard drive - all you get is an error message - "unmountable_boot_volume" - I looked it up and it's due to Microsoft not wanting you booting Windows 2000 or higher from an external drive.
You probably can't install 2000 or XP from a regular Windows CD in a USB optical drive because the contents of the CD cannot recognize most if not all USB optical drive models - the CD boots but all you get is a blue screen. In that case, even if you load the initial files with the set of floppies intended for computers that can't boot from a CD, you still the blue screen.