as already said, you now have a full brick.
gh5 comes with the 3.4 system menu, and an updated ios56.
when you upgraded to system menu 4, it turned ios50 into a stub ios. then you downgraded to 3.2, and ios50 was left as a stub, as it isnt needed by system menu 3.2. then you installed the update on the gh5 disk, which was 3.4. when the update ran, it saw you had a newer ios50 than on the disk, so it skipped installing the old one. unfortunantly for you, the version you have is a stub ios, hence the system menu cant load, hence why you now have a nice white brick.
yet another case of why downgrading is retarded.
you should have had some form of protection from this, be it good brick protection (bootmii as boot2 is the best, preloader wont help this form of brick), or blocking updates(preloader or startpatch can help with this, as can a decent modchip that blocks updates), or simply brick blocking the disk itself.