Did you have the HDd as the first device in the boot order when you loaded the OS and did you have any other devices install (like a USB key fob?)
If you later remove that device, these goes the boot sector. Reinstall it and it works again.
Sorry, I am not good enought at Linux to tell you how to fix it short of reloading the OS again.
No, there are no other devices connected. HD is the first and only one in the boot order.