Linuxcnc 2.4.5 with Ubuntu 10.04, Correct file path or structure ?

There is nothing on the Hard Drive except Ubuntu

Do you have any other older PC?
You can install everything on another PC then move the drive to the machine PC and it just works 98% of the time.
What is the PC make/model?
Try pressing F12 for Dell (F8 for Asus and F11 for some others) with the USB inserted and right after powering on, see if it shows a bootable device list.
Try a different USB, i refuse to believe any PC after roughly 2002 will not boot from USB, even earlier PC's mostly boot from USB without issues.
Is the HDD a PATA or SATA?
PATA = 40 or 80 wire flat cable
SATA = small connector with thin wire, usually black or red color.

I will try that tommorrow , There is no real Identification on the PC, Small Black Box , Has a Motherboard and a Hard drive only.