SeaBIOS is a pure classical BIOS (no UEFI!), so it relies on MBR to boot from Hard Drive. I have experienced the following problem: 1) Qubes R3.1 boots fine instantly after the installation; also, if to upgrade R3.1 to R3.2 - will boot fine as well 2) meanwhile, 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")
After I fixed MBR/GRUB with the steps above, Qubes R3.2 boots perfectly! Although without GRUB graphical themes - the whole booting process (including the moment when you are asked to enter a Qubes partition password) will be a pure text... but it works! :) Dont worry: starting with a graphical login screen, (where you need to choose a user and enter password), you will see the "nice graphics" again. Everything else is normal and works OK ! :) Have not encountered any other problems yet...
qubes-hcl-report told that my hardware/software configuration got all the important features working: HVM, IOMMU, and even SLAT (thanks to A10-5750M APU which supports NPT) https://www.qubes-os.org/news/2016/09/02/4-0-minimum-requirements-3-2-extended-support/ - Minimum requirements of Qubes 4.0 have been met by this AMD-based system
P.S. Going to make a pull request to qubes-hcl repository - HCL report (.yml file)