Booting from an external USB drive is not available on some computers and on those computers where it is workable, you'll need to change the settings in the BIOS so it can boot from USB. (You'll need to check for the USB settings, not just the boot order. On this computer it's under "Legacy Support" in the BIOS and it must be enabled.) Unfortunately, problems frequently occur even when it will boot from USB.
Here, we always fix the DVD/CD drive first, (they're not expensive and it's an easy fix), then make it the first drive in the boot order, and install the OS..
Hope this helps.
I have a dell inspiron 1720 laptop running Vista and it needs to be reformatted badly!! My problem is the internal cd drive doesn't work any longer, so I use an external drive for whenever I need to run a cd. How can I do a reformat using the external drive? I went into setup and changed the boot sequence, but it didn't work.