TL;DR : After converting a dual-boot Ubuntu to UEFI mode, Windows boots correctly, but Ubuntu doesn't gets after the "Loading initial ramdisk" screen. A live usb stick runs perfectly though.
I installed Ubuntu 13.04 64bits via a live usb stick on a ubuntu-enthusiast-cousin's Asus R500D.
It has Windows 7 preinstalled with UEFI support. Sadly, I didn't knew about UEFI and stuff, so I booted the stick in legacy mode, installed Ubuntu without Bios partition and boot-repaired to convert grub to UEFI grub.
But it doesn't get past the "Loading initial ramdisk" line.
I searched and found the UEFI megathread http://ubuntuforums.org/showthread.php?t=2147295 and tried the nomodeset and radeon.nomodeset=0 options, but it didn't work.
I tried to purge the kernels via boot-repair and verified the kernel and initrd files availability in grub with the tab completion (grub edit)
Here's the boot-info : http://paste.ubuntu.com/6147522/
When I try to boot the stick in uefi mode, I only get a black screen after the grub menu, whether I'm trying the install or the "try ubuntu" option. Booting in legacy mode is correct. I tried to disable the UEFI in the BIOS, but then, the PC can't boot in anything (doesn't show even grub)
Sadly, I'm pretty much out of ideas. Anyone has an idea?