Booting from a USB drive that was originally a boot drive

When Win 7 went RTM, I upgraded my laptop from XP. But to protect myself against the possibility of having data inaccessible, I got a new disk and put it in the laptop, and took the old (XP) disk and put it in a USB enclosure.

I have no trouble accessing the data on the USB drive under Windows 7. But I would like to be able to plug it in, tell the BIOS to boot from the USB drive, and be back on my old machine. The laptop is a Dell Precision M90, and it has a boot from USB option in its boot menu. But when I try to do that, it does read the drive, gets as far as putting up the Windows XP splash screen and starting the boot progress bar, and then reboots.

What do I need to do to the old disk now running on USB to allow the machine to boot from it?

Solution 1:

Startup in Safe Mode with boot logging and see if you can identify where Windows fails in booting. You may then refer to the Ntbtlog.txt log file generated in the system root on the external hard drive to further diagnose the problem.

Solution 2:

Pop in your XP CD and do a repair installation (see below), with the USB device connected and set as the active boot device. Where you have swapped from an IDE/AHCI connection to a USB connection, Windows may have got into a twist.

1. When the Press any key to boot from CD message is displayed on your screen, press a key to start your computer from the Windows XP CD.
2. Press Enter when you see the message To setup Windows XP now, and then press Enter displayed on the Welcome to Setup screen.
3. Do not choose the option to press R to use the Recovery Console.
4. In the Windows XP Licensing Agreement, press F8 to agree to the license agreement.
5. Make sure that your current installation of Windows XP is selected in the box, and then press R to repair Windows XP.
6. Follow the instructions on the screen to complete Setup.

I have seen the infinite boot-cycle problem before and the repair installation has usually fixed it.

EDIT - Your next step could be to try FIXBOOT and then FIXMBR in that order from the Recovery Console, after booting into your XP CD again. I would definitely ensure your Windows 7 disk is disconnected for this step. If you are still then unable to boot into XP from your USB-connected XP disk, see if you then have the option to do the repair installation.