I have a new computer with DH87MC board, customer uses 4 USB drives. It will not reliably post with all the drives plugged in. It may work 4 times then fail. When it fails the intel logo pops up then before the function keys display for setup/boot it shuts down, screen goes blank, fans stop then it starts back up and displays error that post failed and press y to enter setup no to continue, pressing no just starts the cycle again and it fails again. The only way to get it to stop failing is to unplug 1 or 2 of the drives and restart pc. It doesn't seem to matter what drives are plugged to what ports. I have had the issue with 3 drives and 4 drives but it always seems to post with only 2 drives attached. If you plug the drives in after boot windows sees all of the drives.
I have updated the bios, tried plugging the drives into a powered hub, turned off legacy usb.
I have also turned off boot to usb, since everyone is convinced it is a boot order problem but since it isn't posting I don't think it should matter. The pc has 3 internal hard drives.
I am running out of ideas to fix the problem