Hello, I have a SONY Vaio laptop with Windows 7 OS. Last night while watching a [streaming] movie, something happened and the movie vanished and then I powered down the laptop. When I power-up, after a while I only get the message "No operating system found." Is there a virus which does this specifically or is made to appear as a hardware failure? How do I do a BIOS boot/check, which key to press repeatedly?