I had connected my laptop to an external display via an HDMI cable in the developers preview of Windows 8.
After sometime I sent the laptop to hibernate mode, without disconnecting the HDMI cable. The next time I switched my laptop on, the screen was not working. I have tried to clone the display as well as extend it without any avail.
My only mode of viewing my laptop is via the HDMI external display again. Restarting the laptop also proves useless as the BIOS screen is also not displayed while booting up.