This is sometimes due to having your hard drive unplugged from the motherboard. unplug and replug the cords for the hard drive. This will ensure they are securely seated.
This can be also be caused by a file that is corrupted in the MBR. You can try booting from a windows disk and choosing the repair option, then typing in SFC /scannow
If you are able to boot into safe mode, do it with command prompt and you can run the same command, but sometimes it doesn't work as well.