Sorry that the replies here are not very fast. This is a small community of busy people…
Looks similar to these issues: Boot device not recognized after installing, how to fix this through rescue mode, "No Bootable Device" after Qubes OS installation, "No bootable device found" After completing qubes os install. There are a few possible solutions in there.
This might be the reason: [qubes-users] New mailing list posting policy.