Remembered later I encountered this issue on a fresh 3.2 install, maybe
you are hitting it too. This does not apply if you are doing UEFI boot,
only GRUB. Found a fix in
https://groups.google.com/forum/?_escaped_fragment_=msg/qubes-users/TS1zfKZ7q8w/JQFkVF4xBgAJ#!msg/qubes-users/TS1zfKZ7q8w/JQFkVF4xBgAJ:
"after a Clean Install of Qubes R3.2, it fails to boot - stuck at "Booting
from hard drive:" SeaBIOS message with blinking "_" character, cant reach
GRUB Boot Menu because MBR (or GRUB) is corrupted out-of-the-box. Luckily
it can be fixed: boot from your Qubes R3.2 installation media, go to
"Troubleshooting -> Rescue a Qubes system", after booting to anaconda
installer please choose "1) Continue" (and enter your Qubes partition
password if you chose to encrypt it during install), then enter "chroot
/mnt/sysimage" - and, finally, "grub2-install /dev/sdX" (where X is a
letter for your hard drive with Qubes, in my case it was sda:
"grub2-install /dev/sda")"