After installing Win 8 on my computer that dual boots with Win 7 I tried to update to Win 8.1 .
I did all the 100+ Windows 7 updates then updated to Win 8.1.
After a 3.2GB download (on DSL) the system spent a couple of hours installing itself.
Eventually it re-booted to a blank screen.
I Left it for a while then switched off at the power button. Switched on, still nothing, no bios boot message. blank screen but the monitor was activated (on).
I Turned it off and on at the power switch, and it booted up to bios screen (whew).
Fortunately I had a mirror of both OS's (Win 7 & Win 8) so I got the computer up and running but I seem doomed to never be able to update to Windows 8.1 on this computer.