Hi,
I have read about 20 threads all with similar issues to mine.
I hit f12 select my USB, select YOSEMITE B which is the name of my usb boot disk. I have tried so many flags...GraphicsEnabler=Yes/No, -x, -f, -v, PCIRootUID=1/0, npci=0x2000 and a few others.
Apple logo shows up...loading bar...