My desktop had been working perfectly. Put in 'Hibernate' while I went for lunch, and on return had the following message on the monitor. the screen was locked and I could only press the power button for 5 secs to get the PC to shut down. Tried boot up. Message returned immediately. Tried inserting a Recovery usb stick and re-boot from 5 sec power button shut down. Exactly the same again. Cannot do anything at all. Tried holding F12 and F8 (separately) on boot up - no change.
The message is:"Reboot and select proper boot device or insert boot media in selected boot device and press any key"