Hello! I have a GA-P55M-UD4 currently running mavericks 10.9.5 and have attempted to update to yosemite afew times now. I get stuck everytime after it installs and it reboots again from usb and i choose the yosemite install (hdd) it goes into apple gray screen with progress bar and nothing happens. I waited the most about 1 hour. Did u try anything special when you updated your mavericks? I followed the guide to a T but no luck. Thanks!!