André
I tried your suggestion and chose the formatwithmbr option while performing an install on another HDD.
This made no difference to my problem, so having a look at the boot-from-usb link you provided, I simply changed the boot order so that it booted 1st from the HDD rather than DVD then HDD.
This worked for both GPT and MBR installations.
So for some reason the boot sequence hangs if the dvd is empty and doesn't carry on to the 2nd device in the BIOS's boot order.
Not sure why, but its not a really much of an issue now.
thanks
Alphred