OK, so i installed Ubuntu on a hard drive the other day so i took that hard drive and kept it in my storage (place where i normally keep my hard drives). When i put it back in my computer it was working fine all was good until i tried to change the boot order in the BIOS and boot from USB OR CD i found out that it Ubuntu just ignored this and kept on with the normal booting process i have tried multiple times please what could be the problem. I have not tried to do anything to the hard drive at all
This is an issue with either your BIOS or your boot medium. Xubuntu has no way of preventing your system from booting up off of external media.
Once you configure your boot device order in your BIOS and ensure that you have enabled booting from any sources that you wish to boot from, the BIOS will follow the following process at system startup:
From this process, you can see that, if you have configured your BIOS to boot from USB or CD before your HDD or wherever you have your Xubuntu installation, the entire device upon which you have installed Xubuntu does not factor in to the success of booting off of your USB drive or CD at all.