as said in title I am unable to boot my rig without attaching my external monitor
anybody know why???.. its totally frustrating :s 
HIVE OS latest
Same problem for me , same mobo.
What VGA card you running?
did you disable onboard vga and disable uefi boot?
HI, I have the same problem, did you solve this? thanks
Flash the last bios
Boot. You likely ear some disturbing BIPs, but don’t trust them. The MB boot (at least for me).
But I end up buying this thing (to avoid BIPs) :
fake the mobo and make it think it have a display connected
hi
update bios and select internal graphic in bios
i have test this one and every ok