I am trying to use a Windows 10 PC which was working fine but has not been used for a while, probably a year or more. When I first turned it on I managed to get into the BIOS, reset the time and check hard disks and boot priority. I then rebooted but received error message "Reboot and select proper boot device. Insert boot media in selected boot device and press a key" I realized I might have set the wrong hard disk for my boot drive and tried getting back to the BIOS. I now cannot do anything as monitor keeps saying entering Sleep Mode and shutting down completely. Can anyone advise how I might be able to get out of this vicious circle?