dodger46 :
Can't convince myself that Windows 8 is at fault, here. It must be Hardware or BIOS/UEFI, and something that is not common to both Win 7 and Win 8, like the Fast Startup which only 8 employs. Have you checked for BIOS updates? And would it be worth resetting CMOS, then re-flashing the BIOS with the same version in case yours is corrupt? (If it will let you...)
I've figured out what it was. Incompatibibility with the WiFi card on some level is slowing down the Safe mode with networking boot up. I tested with no additional drives connected (no HDDs and no optical, only solid state) and got instaboot, turned on networking and rebooted, got the brain fart boot again where it took a minute or two on the blank screen.
I am not the only one who's experienced this issue. A quick search of Windows 8 safe mode black screen will get pages of results with others with the same problem. So there's a possibility something somewhere in the code of Windows 8 causes incompatibility (it is running an outdated driver, only because I prefer this driver to the new one). This problem does not occur in normal boot though.
BIOS is all up to date
Don't get me wrong mate, I like 8, it's just these annoyances really get on my nerves (so it turns into a love hate thing) especially when there was no immediate cause for the longest time
EDIT: Wouldn't a corrupted BIOS cause bigger problems? Not entirely sure if I'm brave enough to flash my BIOS or where I'd find the up to date version
On this case I'll put my hands up and say problem exists between chair and keyboard, because if I'd left it a bit longer it would have started (as I proved today)