At the risk of reviving a slightly old thread..
We are having similar issues with a batch of 800 Elites we received over the Summer (we received over 1000 across our estate, and the issue is presenting itself on assorted ones).
From a COLD boot - as in switching it on 1st thing in the morning, we have a set of PCs which boot up saying there's no System disk.
If you CTRL ALT DEL, it continues to say there's no System disk.
If you press the power button and then immediately press it again, the PC will boot correctly.
From then on, you can reboot to your heart's content.
In experiments, I've found that if I power 1st thing in the morning and hit F9 to select the boot device, either the Hard drive AND DVD are missing, or the Hard drive is missing and the CD is present. What is consistent is that at least the Hard drive isn't available.
If I power off and quickly power up, then hit F9 then both CD and HD are available again.
Our replicated BIOS setup is:
UEFI = disabled
Legacy = enabled
Legacy1 = NIC
Legacy2 = Hard drive
(We're in an environment with PXE boot for imaging, so we need the NIC to boot first)
I can replicate the issue by powering down the PC for 2-3 minutes.
I've verified there's no USB pen/HD connected
I've had the hard drive replaced - no difference.
I've had the RAM replaced - no difference.
I've flashed it with the latest BIOS. This DOES cure the issue, but only because it re-enables UEFI and so my PXE boot is no longer available.
Can you please assist?