mint is not in the sudoers file. This incident will be reported.
So, now I'm on report
Yes I just now received the report!
OK so you need root
to add yourself to sudoers file or even to the admin group. Either should work, but you can't become root?
I was afraid that this might happen, but hoped that you would be on the sudoers list. Seems to me that you should by default. This is how things usually are.
**Have you tried pressing the "Esc" key while booting to see if you can get to some type of recovery mode
Time to hack:
Try to boot a live disc
and see if you can access the USB. You should be able to as long as you have an optical drive (which you never did answer me about)?
Or boot the live disc from a different computer that has an optical drive and attach the USB device after booting.
If you can do the above let me know and I'll post the rest of the hack.
Otherwise you may need to re-install to the USB device next time making sure you have root access.
Please let me know.