Boot from external drive

3035 is not a valid notebook model number -- let's start with the correct one.

If it's a recent system (last 2-3 years), chances are it's UEFI-only.  If you have a UEFI bootable external drive, pressing F12 at powerup will show the drive in the boot menu.  That's dependent on the drive being UEFI bootable.

Most default Linux distributions other than very new ones from specific distributors are not UEFI-bootable.  They can often be made to boot a UEFI-only system, but they're not by default.

@CentreBoy  Due to differences in how the UEFI boot process, temporarily connected UEFI-bootable devices are not listed in the "permanent" boot order in the BIOS Setup.  That interface only lists boot sources that have been registered into the UEFI firmware, which is something normally done automatically by an OS installation routine but which would not have been done for a temporarily connected disk.  To see boot options on temporarily connected devices, use the F12 one-time boot menu.  If you don't see it there either, make sure you actually set up the bootable device properly to support UEFI booting.  Also, if you're trying to boot from an external HDD/SSD rather than a flash drive, some systems only support booting from USB "removable storage class" devices like flash drives, and not USB "fixed disk class" devices like HDDs/SSDs.

jphughan, thanks for your time. I found out that I could get the repair reinstall done another way which didn't require changing the boot order. I'll keep what you said in mind for the future, though.

Again, thanks.