14.04 boot failure with USB disk on HP

Try the boot option:

radeon.nomodeset=1

Do you mean to get a tty and enter that?

https://help.ubuntu.com/community/BootOptions

No, the boot option should be added to the grub.cfg line on the "linux" line at the "quiet splash" location on the line.
But for a UEFI machine, you really should have used gpt partitioning on the USB, have a 500M Fat32 partition with the boot flag for an EFI partition. Install the grub boot loader there (It should go into /EFI/ubuntu, along with the shim.efi file if you want secure boot. The install in UEFI mode should install grub-efi, not the legacy grub-pc package. Then, since the USB is a "removable" device, and the EFI menu will let you select it, you should copy the boot program(s) into /EFI/Boot/bootx64.efi. (Thats a rename of the grubx64.efi for non-secure boot). For secure boot, copy both the shim.efi renamed as bootx64.efi and the signed copy of grubx64.efi. The grub.cfg file used will be in /EFI/ubuntu. boot-repair does this sort of thing for you, but you can copy the files yourself. The EFI menu (some function key) should list ubuntu (and windows), choosing ubuntu should result in a grub

All of the above assume that I can get a terminal to work and that I can get thence to edit.

If you hold SHIFT at boot, you can add the boot option for the single boot. You don't need to edit any files.

OK so I have got it to work - FINALLY and after a day or so of work here and talking to colleagues elsewhere. to all many thanks.

Upshot: This is a UEFI issue (which really should be sorted by now) combined with some issues with grub and possibly something in the kernel and there appears to be some reason that it doesn't apply h/w acceleration. The h/w isn't special and grub ought to be able to cope with it (if M$ can why can't Linux?). The difference made by booting into an old version of the kernel suggests that there is a bug somewhere there that needs attention.

I am offering the following as INFORMATION, to give people clues as to what they may need to do if they find themselves in a similar situation:

My starting point is as per the original question (above). I point out that the .iso file was downloaded from Ubuntu's main page and Startup Disk Creator was used to make it a live USB disk.

I managed to get a text line after several attempts and the combination of radeon.nomodeset=1 and acpi_osi = AFTER "quiet splash" in the boot file settings got rid of many of the problems and I could at least get a screen that was purple. BUT it didn't get any further.

[I thoroughly recommend http://ubuntuforums.org/showthread.php?t=1613132 as a guide to what these parameters do]

I finally got it to work by rebooting, going to recovery mode, booting in 3.13.0.24 (I had .27 generic installed originally). Using Advanced Ubuntu settings enabled editing of the grub config file to set the parameters as above. This finally got me to UNITY :-(

Downloading updates stabilised the system and enabled me to reboot consistently to Unity, although the 10px-wide.

Interestingly enough in the middle of all this I got the message from Tahr that "...your real question maybe why X didn't use hardware acceleration for your system"! Suggestions anyone?

I wondered if anyone had a comment on the last two lines. Particularly as I received the following mail overnight...

".... We were wondering if this is still an issue? If
so, could you please test for this with the latest development release
of Ubuntu? ISO images are available from http://cdimage.ubuntu.com
/daily-live/current/ .

....."

In my particular case the work around has worked, BUT performance is poor as battery life isn't brilliant.

If you create a new question we can help with the battery life issue

OK thanks, will do...later this pm.