I am having a nearly identical problem trying to install Mageia 4.1 Full from USB on a UEFI machine with dual-boot to Windows 8.
There's a bug submitted here that might be identical to your experience:
https://bugs.mageia.org/show_bug.cgi?id=13471To add context, I click on "Install Mageia" and Xorg finally loads after 60+ seconds of failure, then only the left half of the screen is visible when the next installation menu in displayed.