sorry, I've made a mistake typing the partition names...

I have followed the same procedure I wrote but with the right names for partitions and I get the same result. I'm going to try what you have posted. Thanks

I think one characteristic of the boot system is that it will go to track zero sector zero and try to boot from there even without grub. perhaps there is a way to copy the boot program so it starts at track 0 sector 0. ( or maybe it is the beginning track/sector if 0/0 is not right. )

Try this first:
Usually USB disks are recognized as Hard disk drives by the BIOS.
In this case the HDD should be first in boot order.If the USB drive is listed in this menu make sure its in 1st position.

These days most of the bios has another menu to set the HDD order. If this is the case make sure that HDD is the first boot device and then make the USB as the 1st HDD in the HDD order menu.

If the above fails, the USB u created is not bootable. You may try the following:
I usually use the DD command to create boot able USBs rather than UNetBootIn. DD command to create boot able disks has worked for me in most cases. The command is simple:

dd if=/path/to/iso/image of=/dev/sdx
Make sure to use /dev/sdx and not /dev/sdx1
'x' is the alphabet of your USB drive

Thank you firewiz87, I will try that at the weekend and I will post the answer.