Reboot and Select proper boot device or Insert boot media in selected boot device
Solution 1:
Guess what, I had this problem when I got up to switch on my machine this morning at 03.26. As I was reading Mepher's answers I kept on switching on and off my computer and at the same time unplugging from the wall socket and plugging again. Repeating this process several times all the time and bingo I got the machine back on track. You need to be patient though. good luck. Please give me a feedback to this suggestion.
Solution 2:
Is there a USB stick on your computer which you may have forgotten to unmount?
If your answer is no, I'm going to ask you if you have installed any new hardware to your PC lately. This may be the reason of the error. If so, disconnect any new hardware that you have installed, then start the computer and keep pressing F8, then when the boot screen comes up, select Safe Mode. Afterwards, just wait for it to load up and then run System Restore.
Waiting for your feedback.
Solution 3:
Have you double-checked that your computer is booting to your hard drive and not some other device? It's possible your bios decided to try booting to something else after a power failure. To do so, just pick your boot device (it varies by computer manufacturer; usually mashing the F-keys along with the Del key during boot will hit it). Then, pick to boot from your hard drive.