Boot from external usb hard drive on Dell Inspiron 4100

I have a Dell Inspiron 4100 laptop and I just bought an external 3.5" usb enclosure for my 120GB Sata drive. The external hard drive has windows installed but I am not sure how to get it to boot. I looked in the BIOS to see if there was any settings that would allow me to boot from external device but didnt see any.

The reason why I bought the enclosure was my Pentium 4 proc died and Windows crashed on me.  I feel windows may be corrupt but want to attempt to boot to the external drive to see.  I would like to get windows reinstalled on that drive so I dont have to spend years reloading a pre service pack 1 XP pro disc and all the millions of updates it takes to get it updated.

Any other options on booted to this device from the Dell laptop?
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zephyr_hex (Megan)Connect With a Mentor DeveloperCommented:
i would recommend updating your BIOS.
zephyr_hex (Megan)DeveloperCommented:
oh yeah, and make sure the external hdd is FIRST in your boot sequence in BIOS
It seems this kind of question (booting windows from an external unit) is very common right now. It also seems the usual answer is "windows can't do this", i.e. boot off an external unit. If this windows installation you mention is done on another computer, it will not run in a useful way on different hardware anyway, even if it *could* boot from this external enclosure. I guess your best option is to replace the fautly CPU and do a repair on your O/S installation.
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To boot from and external USB device you will need to go into BIOS or if a one time selection is available by pressing F12 you mibe able to.  However as indicated by rid, a multitude of issues/problems exist.  Obvious questions would be:

Was the software loaded onto the External Drive by that laptop or an Identical one?  If NO - problems exist.

Is XP loaded on the External Drive?  If YES - problems exist.

If you want to obtain data from the HD in the Laptop it might be a better choice to obtain an External Enclosure for that HD and attach to another computer to extract the information from.  Following is a link to a selection of Enclosures.  Of interest is some require and external power source, while others require either one or two USB plugs.

Hope this Helps!!!

some points :
- to be able to boot from a usb device, your BIOS must allow it. if it does not allow it, the only option is to use a PCI to usb card.
-what was wrong with your system first? - if you replaced the cpu, what happens?
-what are you trying to do with that external drive ?
it is not clear from your comment : "so I dont have to spend years reloading a pre service pack 1 XP pro disc and all the millions of updates it takes to get it updated"
if you want to install a fully updated version of XP, i suggest using a "slipstreamed" cd :
As rid has already mentioned, you won't be able to boot into windows from a USB drive. You could get into a "prewindows", like the installation routine of windows, but you can't actually install it because the drivers needed to go on don't exist.
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