After several tries I managed to install Ubuntu 12.04 in EFI mode (GPT partition table) on my DELL Inspiron 15z. What worked for me is what is in this post http://askubuntu.com/a/224332/149034, i.e. I set the BIOS in legacy mode and then choose to boot (F12 at stuart-up) the 12.04 Live CD in EFI mode. In this way I get Ubuntu installed in a GPT partition table , with EFI boot loader.
The problem is that now, to start Ubuntu, I have to repeat these steps everytime:
The boot is set in legacy mode from BIOS.
I press F12 at start-up to choose to boot Ubuntu in UEFI mode.
If I set UEFI mode directly in BIOS, after grub, I get a blank (purple) screen, and Ubuntu does not start.
Secure boot is disabled, and I tried fixing it with boot-repair but did not succeed.
Does anyone have a clue of what is the problem?
I discovered this is related to a bug
https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1093472 https://answers.launchpad.net/ubuntu-certification/+question/217551 Ubuntu 12.10 boot hangs at purple screen when integrated NIC (ethernet card) is enabled in BIOS
it turns out that deactivating integrated NIT in BIOS the UEFI boots starts directly. But wirh no ethernet....