Bump, I've got same issue now
Same here. I've narrowed it down to USB drives that are GPT formatted. Specifically, my 4TB drives. The 2TB are all formatted with MBR, and they do not interfere with the boot process. But the GPT will cause the system to hang during post. To be precise, right after BIOS detects the internal SATA and the SATA DVD burner. I have to unplug the 4TB drive, reboot, and once the W8 flag is showing, I can plug it back in again.
I cannot believe how many people I've found posting this same issue, and none of the threads are completed with a solution. How does one tell the PC (BIOS, windows boot manager,???) to exclusively boot from a specific (internal SATA) drive??