Reboot and select proper boot device or insert boot media in selected boot devic

The solution is to reboot and select the proper boot device, or make the selected boot device bootable.... Not a lot else to say since it told you what to do... If it was working then remove any usb drives and CDs, make sure your OS drive is connected and selected as your boot drive...

If you were trying to create a dual boot machine you probably screwed up and need to repair the boot record, but you didn't give us any information on your system