Mid-2012 15" Retina blank screen when booting from USB
I am trying to create a Yosemite bootable USB for a mid-2012 15" MacBook Pro Retina but whenever I try to boot from it the screen just stays black but the backlight is on. The machine still has a working version of Yosemite on it and recovery mode boots just fine and I can select the USB as a startup disk but upon restart it's just a backlit blank screen. Resetting the PRAM does not help.
The USB itself was created by downloading the Yosemite installer onto a mac mini running 10.6.8 and I carefully (and repeatedly) have followed the instructions using disk utility (GUID partition, etc...). When I try to boot from the USB I can see the USB's led flashes for 1-2 seconds but then stops suggesting it's not reading/loading it.
Any help would be much appreciated.
MacBook Pro with Retina display, OS X Yosemite (10.10.4)